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 $58.41   7.281%   $62.6628   $62.66   $62.65   $62.70  
  Purchase #2 $117.92   11.531%   $131.5174   $131.52   $131.50   $131.50  
  Purchase #3 $148.59   3.217%   $153.3701   $153.37   $153.35   $153.40  
  Purchase #4 $124.52   7.319%   $133.6336   $133.63   $133.65   $133.60  
  Purchase #5 $65.99   8.409%   $71.5391   $71.54   $71.55   $71.50  
  Purchase #6 $10.99   7.263%   $11.7882   $11.79   $11.80   $11.80  
  Purchase #7 $206.87   13.483%   $234.7623   $234.76   $234.75   $234.80  
  7 purchase totals = $733.29       $799.2735   $799.27   $799.25   $799.30