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 $214.86   13.651%   $244.1905   $244.19   $244.20   $244.20  
  Purchase #2 $84.52   11.668%   $94.3818   $94.38   $94.40   $94.40  
  Purchase #3 $169.54   9.537%   $185.709   $185.71   $185.70   $185.70  
  Purchase #4 $100.67   6.425%   $107.138   $107.14   $107.15   $107.10  
  Purchase #5 $38.89   3.871%   $40.3954   $40.40   $40.40   $40.40  
  Purchase #6 $173.26   6.385%   $184.3227   $184.32   $184.30   $184.30  
  Purchase #7 $243.79   11.645%   $272.1793   $272.18   $272.20   $272.20  
  7 purchase totals = $1,025.53       $1,128.3167   $1,128.32   $1,128.35   $1,128.30