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 $127.46   6.628%   $135.908   $135.91   $135.90   $135.90  
  Purchase #2 $205.69   3.521%   $212.9323   $212.93   $212.95   $212.90  
  Purchase #3 $46.45   7.400%   $49.8873   $49.89   $49.90   $49.90  
  Purchase #4 $116.56   3.449%   $120.5802   $120.58   $120.60   $120.60  
  Purchase #5 $225.33   7.180%   $241.5087   $241.51   $241.50   $241.50  
  Purchase #6 $11.61   9.594%   $12.7239   $12.72   $12.70   $12.70  
  Purchase #7 $236.39   11.420%   $263.3857   $263.39   $263.40   $263.40  
  7 purchase totals = $969.49       $1,036.9261   $1,036.93   $1,036.95   $1,036.90