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 $163.82   7.298%   $175.7756   $175.78   $175.80   $175.80  
  Purchase #2 $76.72   11.283%   $85.3763   $85.38   $85.40   $85.40  
  Purchase #3 $115.90   7.111%   $124.1416   $124.14   $124.15   $124.10  
  Purchase #4 $24.64   3.200%   $25.4285   $25.43   $25.45   $25.40  
  Purchase #5 $215.82   6.763%   $230.4159   $230.42   $230.40   $230.40  
  Purchase #6 $109.77   13.204%   $124.264   $124.26   $124.25   $124.30  
  Purchase #7 $145.42   3.530%   $150.5533   $150.55   $150.55   $150.60  
  7 purchase totals = $852.09       $915.9552   $915.96   $916.00   $916.00