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 $188.93   8.796%   $205.5483   $205.55   $205.55   $205.50  
  Purchase #2 $199.68   11.303%   $222.2498   $222.25   $222.25   $222.20  
  Purchase #3 $97.40   4.225%   $101.5152   $101.52   $101.50   $101.50  
  Purchase #4 $178.93   10.641%   $197.9699   $197.97   $197.95   $198.00  
  Purchase #5 $94.54   6.693%   $100.8676   $100.87   $100.85   $100.90  
  Purchase #6 $49.98   5.740%   $52.8489   $52.85   $52.85   $52.80  
  Purchase #7 $70.93   6.672%   $75.6624   $75.66   $75.65   $75.70  
  7 purchase totals = $880.39       $956.6621   $956.67   $956.60   $956.60