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 $56.92   5.195%   $59.877   $59.88   $59.90   $59.90  
  Purchase #2 $194.41   6.651%   $207.3402   $207.34   $207.35   $207.30  
  Purchase #3 $151.43   6.475%   $161.2351   $161.24   $161.25   $161.20  
  Purchase #4 $197.70   6.153%   $209.8645   $209.86   $209.85   $209.90  
  Purchase #5 $123.75   8.228%   $133.9322   $133.93   $133.95   $133.90  
  Purchase #6 $25.95   12.514%   $29.1974   $29.20   $29.20   $29.20  
  Purchase #7 $196.99   12.417%   $221.4502   $221.45   $221.45   $221.50  
  7 purchase totals = $947.15       $1,022.8966   $1,022.90   $1,022.95   $1,022.90