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 $131.93   11.182%   $146.6824   $146.68   $146.70   $146.70  
  Purchase #2 $80.65   12.841%   $91.0063   $91.01   $91.00   $91.00  
  Purchase #3 $133.55   7.345%   $143.3592   $143.36   $143.35   $143.40  
  Purchase #4 $237.72   10.411%   $262.469   $262.47   $262.45   $262.50  
  Purchase #5 $238.92   8.385%   $258.9534   $258.95   $258.95   $259.00  
  Purchase #6 $151.64   10.315%   $167.2817   $167.28   $167.30   $167.30  
  Purchase #7 $23.63   9.130%   $25.7874   $25.79   $25.80   $25.80  
  7 purchase totals = $998.04       $1,095.5394   $1,095.54   $1,095.55   $1,095.70