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 $208.53   7.276%   $223.7026   $223.70   $223.70   $223.70  
  Purchase #2 $196.79   13.138%   $222.6443   $222.64   $222.65   $222.60  
  Purchase #3 $19.48   5.737%   $20.5976   $20.60   $20.60   $20.60  
  Purchase #4 $81.34   4.123%   $84.6936   $84.69   $84.70   $84.70  
  Purchase #5 $205.80   11.481%   $229.4279   $229.43   $229.45   $229.40  
  Purchase #6 $186.53   4.404%   $194.7448   $194.74   $194.75   $194.70  
  Purchase #7 $125.52   10.468%   $138.6594   $138.66   $138.65   $138.70  
  7 purchase totals = $1,023.99       $1,114.4702   $1,114.46   $1,114.50   $1,114.40