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 $91.44   3.536%   $94.6733   $94.67   $94.65   $94.70  
  Purchase #2 $10.54   7.213%   $11.3003   $11.30   $11.30   $11.30  
  Purchase #3 $204.27   6.175%   $216.8837   $216.88   $216.90   $216.90  
  Purchase #4 $36.63   7.723%   $39.4589   $39.46   $39.45   $39.50  
  Purchase #5 $231.76   4.591%   $242.4001   $242.40   $242.40   $242.40  
  Purchase #6 $125.87   13.649%   $143.05   $143.05   $143.05   $143.10  
  Purchase #7 $150.96   6.564%   $160.869   $160.87   $160.85   $160.90  
  7 purchase totals = $851.47       $908.6353   $908.63   $908.60   $908.80