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 $68.35   3.311%   $70.6131   $70.61   $70.60   $70.60  
  Purchase #2 $132.82   12.756%   $149.7625   $149.76   $149.75   $149.80  
  Purchase #3 $205.80   8.147%   $222.5665   $222.57   $222.55   $222.60  
  Purchase #4 $155.95   3.841%   $161.94   $161.94   $161.95   $161.90  
  Purchase #5 $12.65   10.340%   $13.958   $13.96   $13.95   $14.00  
  Purchase #6 $147.67   13.645%   $167.8196   $167.82   $167.80   $167.80  
  Purchase #7 $36.79   11.351%   $40.966   $40.97   $40.95   $41.00  
  7 purchase totals = $760.03       $827.6257   $827.63   $827.55   $827.70