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 $88.71   11.232%   $98.6739   $98.67   $98.65   $98.70  
  Purchase #2 $177.33   12.218%   $198.9962   $199.00   $199.00   $199.00  
  Purchase #3 $85.58   7.304%   $91.8308   $91.83   $91.85   $91.80  
  Purchase #4 $27.73   4.853%   $29.0757   $29.08   $29.10   $29.10  
  Purchase #5 $39.82   5.731%   $42.1021   $42.10   $42.10   $42.10  
  Purchase #6 $140.41   3.234%   $144.9509   $144.95   $144.95   $145.00  
  Purchase #7 $241.93   10.293%   $266.8319   $266.83   $266.85   $266.80  
  7 purchase totals = $801.51       $872.4615   $872.46   $872.50   $872.50