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 $20.66   9.408%   $22.6037   $22.60   $22.60   $22.60  
  Purchase #2 $19.96   10.579%   $22.0716   $22.07   $22.05   $22.10  
  Purchase #3 $249.65   8.333%   $270.4533   $270.45   $270.45   $270.50  
  Purchase #4 $131.52   11.351%   $146.4488   $146.45   $146.45   $146.40  
  Purchase #5 $168.84   9.756%   $185.312   $185.31   $185.30   $185.30  
  Purchase #6 $7.55   10.432%   $8.3376   $8.34   $8.35   $8.30  
  Purchase #7 $138.93   12.470%   $156.2546   $156.25   $156.25   $156.30  
  7 purchase totals = $737.11       $811.4816   $811.47   $811.45   $811.50