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 $86.86   8.231%   $94.0094   $94.01   $94.00   $94.00  
  Purchase #2 $110.92   7.861%   $119.6394   $119.64   $119.65   $119.60  
  Purchase #3 $101.39   3.373%   $104.8099   $104.81   $104.80   $104.80  
  Purchase #4 $81.76   9.872%   $89.8313   $89.83   $89.85   $89.80  
  Purchase #5 $31.59   11.251%   $35.1442   $35.14   $35.15   $35.10  
  Purchase #6 $171.59   4.323%   $179.0078   $179.01   $179.00   $179.00  
  Purchase #7 $184.34   9.421%   $201.7067   $201.71   $201.70   $201.70  
  7 purchase totals = $768.45       $824.1487   $824.15   $824.15   $824.00