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 $99.78   8.699%   $108.4599   $108.46   $108.45   $108.50  
  Purchase #2 $27.94   5.860%   $29.5773   $29.58   $29.60   $29.60  
  Purchase #3 $93.84   5.608%   $99.1025   $99.10   $99.10   $99.10  
  Purchase #4 $103.25   5.360%   $108.7842   $108.78   $108.80   $108.80  
  Purchase #5 $146.59   8.463%   $158.9959   $159.00   $159.00   $159.00  
  Purchase #6 $65.58   7.487%   $70.49   $70.49   $70.50   $70.50  
  Purchase #7 $216.31   9.744%   $237.3872   $237.39   $237.40   $237.40  
  7 purchase totals = $753.29       $812.7970   $812.80   $812.85   $812.90