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 $88.44   6.674%   $94.3425   $94.34   $94.35   $94.30  
  Purchase #2 $191.79   4.432%   $200.2901   $200.29   $200.30   $200.30  
  Purchase #3 $107.66   9.441%   $117.8242   $117.82   $117.80   $117.80  
  Purchase #4 $236.72   9.636%   $259.5303   $259.53   $259.55   $259.50  
  Purchase #5 $86.92   5.204%   $91.4433   $91.44   $91.45   $91.40  
  Purchase #6 $37.26   8.315%   $40.3582   $40.36   $40.35   $40.40  
  Purchase #7 $192.99   7.641%   $207.7364   $207.74   $207.75   $207.70  
  7 purchase totals = $941.78       $1,011.5250   $1,011.52   $1,011.55   $1,011.40