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 $61.81   13.292%   $70.0258   $70.03   $70.05   $70.00  
  Purchase #2 $86.32   13.480%   $97.9559   $97.96   $97.95   $98.00  
  Purchase #3 $88.64   8.765%   $96.4093   $96.41   $96.40   $96.40  
  Purchase #4 $204.81   11.735%   $228.8445   $228.84   $228.85   $228.80  
  Purchase #5 $194.29   5.843%   $205.6424   $205.64   $205.65   $205.60  
  Purchase #6 $27.26   12.310%   $30.6157   $30.62   $30.60   $30.60  
  Purchase #7 $91.63   11.166%   $101.8614   $101.86   $101.85   $101.90  
  7 purchase totals = $754.76       $831.3550   $831.36   $831.35   $831.30