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 $24.41   4.723%   $25.5629   $25.56   $25.55   $25.60  
  Purchase #2 $239.67   13.535%   $272.1093   $272.11   $272.10   $272.10  
  Purchase #3 $98.30   6.326%   $104.5185   $104.52   $104.50   $104.50  
  Purchase #4 $65.47   5.162%   $68.8496   $68.85   $68.85   $68.80  
  Purchase #5 $122.97   13.129%   $139.1147   $139.11   $139.10   $139.10  
  Purchase #6 $119.58   8.544%   $129.7969   $129.80   $129.80   $129.80  
  Purchase #7 $244.79   12.528%   $275.4573   $275.46   $275.45   $275.50  
  7 purchase totals = $915.19       $1,015.4092   $1,015.41   $1,015.35   $1,015.40