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 $54.91   10.690%   $60.7799   $60.78   $60.80   $60.80  
  Purchase #2 $110.33   12.354%   $123.9602   $123.96   $123.95   $124.00  
  Purchase #3 $59.31   9.286%   $64.8175   $64.82   $64.80   $64.80  
  Purchase #4 $46.48   8.547%   $50.4526   $50.45   $50.45   $50.50  
  Purchase #5 $54.54   12.351%   $61.2762   $61.28   $61.30   $61.30  
  Purchase #6 $194.67   3.693%   $201.8592   $201.86   $201.85   $201.90  
  Purchase #7 $191.29   4.338%   $199.5882   $199.59   $199.60   $199.60  
  7 purchase totals = $711.53       $762.7338   $762.74   $762.75   $762.90