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 $193.61   3.808%   $200.9827   $200.98   $201.00   $201.00  
  Purchase #2 $232.68   13.377%   $263.8056   $263.81   $263.80   $263.80  
  Purchase #3 $194.29   9.783%   $213.2974   $213.30   $213.30   $213.30  
  Purchase #4 $5.96   6.305%   $6.3358   $6.34   $6.35   $6.30  
  Purchase #5 $62.27   8.854%   $67.7834   $67.78   $67.80   $67.80  
  Purchase #6 $11.87   12.709%   $13.3786   $13.38   $13.40   $13.40  
  Purchase #7 $56.69   4.861%   $59.4457   $59.45   $59.45   $59.40  
  7 purchase totals = $757.37       $825.0292   $825.04   $825.10   $825.00