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 $55.49   8.160%   $60.018   $60.02   $60.00   $60.00  
  Purchase #2 $19.73   8.553%   $21.4175   $21.42   $21.40   $21.40  
  Purchase #3 $8.74   7.540%   $9.399   $9.40   $9.40   $9.40  
  Purchase #4 $56.77   10.439%   $62.6962   $62.70   $62.70   $62.70  
  Purchase #5 $97.89   8.861%   $106.564   $106.56   $106.55   $106.60  
  Purchase #6 $48.31   12.239%   $54.2227   $54.22   $54.20   $54.20  
  Purchase #7 $203.29   8.543%   $220.6571   $220.66   $220.65   $220.70  
  7 purchase totals = $490.22       $534.9745   $534.98   $534.90   $535.00