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 $93.65   8.672%   $101.7713   $101.77   $101.75   $101.80  
  Purchase #2 $181.30   5.475%   $191.2262   $191.23   $191.25   $191.20  
  Purchase #3 $53.61   3.710%   $55.5989   $55.60   $55.60   $55.60  
  Purchase #4 $165.53   5.680%   $174.9321   $174.93   $174.95   $174.90  
  Purchase #5 $190.98   8.267%   $206.7683   $206.77   $206.75   $206.80  
  Purchase #6 $143.51   11.616%   $160.1801   $160.18   $160.20   $160.20  
  Purchase #7 $125.25   8.702%   $136.1493   $136.15   $136.15   $136.10  
  7 purchase totals = $953.83       $1,026.6262   $1,026.63   $1,026.65   $1,026.60