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 $207.46   11.655%   $231.6395   $231.64   $231.65   $231.60  
  Purchase #2 $136.79   10.196%   $150.7371   $150.74   $150.75   $150.70  
  Purchase #3 $247.65   5.299%   $260.773   $260.77   $260.75   $260.80  
  Purchase #4 $215.30   11.849%   $240.8109   $240.81   $240.80   $240.80  
  Purchase #5 $82.91   5.871%   $87.7776   $87.78   $87.80   $87.80  
  Purchase #6 $9.85   6.715%   $10.5114   $10.51   $10.50   $10.50  
  Purchase #7 $37.57   6.143%   $39.8779   $39.88   $39.90   $39.90  
  7 purchase totals = $937.53       $1,022.1274   $1,022.13   $1,022.15   $1,022.10