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 $88.99   4.456%   $92.9554   $92.96   $92.95   $93.00  
  Purchase #2 $27.85   3.150%   $28.7273   $28.73   $28.75   $28.70  
  Purchase #3 $235.83   4.562%   $246.5886   $246.59   $246.60   $246.60  
  Purchase #4 $41.94   13.461%   $47.5855   $47.59   $47.60   $47.60  
  Purchase #5 $96.31   7.618%   $103.6469   $103.65   $103.65   $103.60  
  Purchase #6 $150.76   8.256%   $163.2067   $163.21   $163.20   $163.20  
  Purchase #7 $64.81   4.566%   $67.7692   $67.77   $67.75   $67.80  
  7 purchase totals = $706.49       $750.4796   $750.50   $750.50   $750.50