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 $41.57   13.526%   $47.1928   $47.19   $47.20   $47.20  
  Purchase #2 $90.92   12.523%   $102.3059   $102.31   $102.30   $102.30  
  Purchase #3 $89.66   11.425%   $99.9037   $99.90   $99.90   $99.90  
  Purchase #4 $102.52   4.586%   $107.2216   $107.22   $107.20   $107.20  
  Purchase #5 $91.48   12.247%   $102.6836   $102.68   $102.70   $102.70  
  Purchase #6 $104.45   5.218%   $109.9002   $109.90   $109.90   $109.90  
  Purchase #7 $141.52   4.635%   $148.0795   $148.08   $148.10   $148.10  
  7 purchase totals = $662.12       $717.2873   $717.28   $717.30   $717.30