Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $30.26   9.572%   $33.1565   $33.16   $33.15   $33.20  
  Purchase #2 $217.93   8.488%   $236.4279   $236.43   $236.45   $236.40  
  Purchase #3 $160.38   13.493%   $182.0201   $182.02   $182.00   $182.00  
  Purchase #4 $250.58   12.150%   $281.0255   $281.03   $281.05   $281.00  
  Purchase #5 $202.80   9.850%   $222.7758   $222.78   $222.80   $222.80  
  Purchase #6 $238.92   5.258%   $251.4824   $251.48   $251.50   $251.50  
  Purchase #7 $206.96   10.340%   $228.3597   $228.36   $228.35   $228.40  
  7 purchase totals = $1,307.83       $1,435.2479   $1,435.26   $1,435.30   $1,435.30