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 $217.45   6.624%   $231.8539   $231.85   $231.85   $231.90  
  Purchase #2 $53.91   6.196%   $57.2503   $57.25   $57.25   $57.30  
  Purchase #3 $59.33   11.406%   $66.0972   $66.10   $66.10   $66.10  
  Purchase #4 $214.90   9.557%   $235.438   $235.44   $235.45   $235.40  
  Purchase #5 $121.98   8.618%   $132.4922   $132.49   $132.50   $132.50  
  Purchase #6 $199.56   9.527%   $218.5721   $218.57   $218.55   $218.60  
  Purchase #7 $74.88   12.874%   $84.5201   $84.52   $84.50   $84.50  
  7 purchase totals = $942.01       $1,026.2238   $1,026.22   $1,026.20   $1,026.30