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 $64.94   7.553%   $69.8449   $69.84   $69.85   $69.80  
  Purchase #2 $198.70   3.174%   $205.0067   $205.01   $205.00   $205.00  
  Purchase #3 $79.53   6.816%   $84.9508   $84.95   $84.95   $85.00  
  Purchase #4 $233.81   4.768%   $244.9581   $244.96   $244.95   $245.00  
  Purchase #5 $76.54   12.733%   $86.2858   $86.29   $86.30   $86.30  
  Purchase #6 $76.40   11.281%   $85.0187   $85.02   $85.00   $85.00  
  Purchase #7 $144.69   4.236%   $150.8191   $150.82   $150.80   $150.80  
  7 purchase totals = $874.61       $926.8841   $926.89   $926.85   $926.90