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 $139.25   9.613%   $152.6361   $152.64   $152.65   $152.60  
  Purchase #2 $90.43   4.644%   $94.6296   $94.63   $94.65   $94.60  
  Purchase #3 $23.60   11.378%   $26.2852   $26.29   $26.30   $26.30  
  Purchase #4 $95.39   7.595%   $102.6349   $102.63   $102.65   $102.60  
  Purchase #5 $194.85   4.702%   $204.0118   $204.01   $204.00   $204.00  
  Purchase #6 $206.75   11.125%   $229.7509   $229.75   $229.75   $229.80  
  Purchase #7 $84.53   11.435%   $94.196   $94.20   $94.20   $94.20  
  7 purchase totals = $834.80       $904.1445   $904.15   $904.20   $904.10