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 $88.61   7.732%   $95.4613   $95.46   $95.45   $95.50  
  Purchase #2 $205.98   8.138%   $222.7427   $222.74   $222.75   $222.70  
  Purchase #3 $137.57   11.781%   $153.7771   $153.78   $153.80   $153.80  
  Purchase #4 $25.78   12.164%   $28.9159   $28.92   $28.90   $28.90  
  Purchase #5 $221.83   4.700%   $232.256   $232.26   $232.25   $232.30  
  Purchase #6 $15.60   8.656%   $16.9503   $16.95   $16.95   $17.00  
  Purchase #7 $84.59   12.119%   $94.8415   $94.84   $94.85   $94.80  
  7 purchase totals = $779.96       $844.9448   $844.95   $844.95   $845.00