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 $57.43   13.634%   $65.26   $65.26   $65.25   $65.30  
  Purchase #2 $155.47   13.355%   $176.233   $176.23   $176.25   $176.20  
  Purchase #3 $184.35   4.546%   $192.7306   $192.73   $192.75   $192.70  
  Purchase #4 $158.49   3.788%   $164.4936   $164.49   $164.50   $164.50  
  Purchase #5 $46.66   9.276%   $50.9882   $50.99   $51.00   $51.00  
  Purchase #6 $165.82   9.723%   $181.9427   $181.94   $181.95   $181.90  
  Purchase #7 $39.79   11.179%   $44.2381   $44.24   $44.25   $44.20  
  7 purchase totals = $808.01       $875.8862   $875.88   $875.95   $875.80