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 $180.27   9.377%   $197.1739   $197.17   $197.15   $197.20  
  Purchase #2 $111.72   11.743%   $124.8393   $124.84   $124.85   $124.80  
  Purchase #3 $235.26   13.451%   $266.9048   $266.90   $266.90   $266.90  
  Purchase #4 $233.30   6.236%   $247.8486   $247.85   $247.85   $247.80  
  Purchase #5 $202.92   9.571%   $222.3415   $222.34   $222.35   $222.30  
  Purchase #6 $147.73   3.145%   $152.3761   $152.38   $152.40   $152.40  
  Purchase #7 $145.30   6.505%   $154.7518   $154.75   $154.75   $154.80  
  7 purchase totals = $1,256.50       $1,366.2360   $1,366.23   $1,366.25   $1,366.20