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 $18.25   8.771%   $19.8507   $19.85   $19.85   $19.90  
  Purchase #2 $24.26   5.402%   $25.5705   $25.57   $25.55   $25.60  
  Purchase #3 $211.96   11.488%   $236.31   $236.31   $236.30   $236.30  
  Purchase #4 $78.88   5.345%   $83.0961   $83.10   $83.10   $83.10  
  Purchase #5 $58.35   8.273%   $63.1773   $63.18   $63.20   $63.20  
  Purchase #6 $245.98   8.757%   $267.5205   $267.52   $267.50   $267.50  
  Purchase #7 $63.87   5.437%   $67.3426   $67.34   $67.35   $67.30  
  7 purchase totals = $701.55       $762.8677   $762.87   $762.85   $762.90