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 $160.54   8.324%   $173.9033   $173.90   $173.90   $173.90  
  Purchase #2 $102.81   3.728%   $106.6428   $106.64   $106.65   $106.60  
  Purchase #3 $119.54   4.186%   $124.5439   $124.54   $124.55   $124.50  
  Purchase #4 $24.26   9.544%   $26.5754   $26.58   $26.60   $26.60  
  Purchase #5 $41.54   4.178%   $43.2755   $43.28   $43.30   $43.30  
  Purchase #6 $184.42   10.722%   $204.1935   $204.19   $204.20   $204.20  
  Purchase #7 $91.58   10.479%   $101.1767   $101.18   $101.20   $101.20  
  7 purchase totals = $724.69       $780.3111   $780.31   $780.40   $780.30