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 $134.68   8.579%   $146.2342   $146.23   $146.25   $146.20  
  Purchase #2 $75.47   8.158%   $81.6268   $81.63   $81.65   $81.60  
  Purchase #3 $63.49   10.699%   $70.2828   $70.28   $70.30   $70.30  
  Purchase #4 $162.27   7.547%   $174.5165   $174.52   $174.50   $174.50  
  Purchase #5 $123.41   7.438%   $132.5892   $132.59   $132.60   $132.60  
  Purchase #6 $165.55   7.362%   $177.7378   $177.74   $177.75   $177.70  
  Purchase #7 $27.98   13.339%   $31.7123   $31.71   $31.70   $31.70  
  7 purchase totals = $752.85       $814.6996   $814.70   $814.75   $814.60