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 $214.59   6.112%   $227.7057   $227.71   $227.70   $227.70  
  Purchase #2 $67.41   13.670%   $76.6249   $76.62   $76.60   $76.60  
  Purchase #3 $203.81   12.560%   $229.4085   $229.41   $229.40   $229.40  
  Purchase #4 $136.42   13.788%   $155.2296   $155.23   $155.25   $155.20  
  Purchase #5 $202.88   12.607%   $228.4571   $228.46   $228.45   $228.50  
  Purchase #6 $88.95   6.192%   $94.4578   $94.46   $94.45   $94.50  
  Purchase #7 $22.70   13.723%   $25.8151   $25.82   $25.80   $25.80  
  7 purchase totals = $936.76       $1,037.6987   $1,037.71   $1,037.65   $1,037.70