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 $148.37   12.721%   $167.2441   $167.24   $167.25   $167.20  
  Purchase #2 $84.85   11.397%   $94.5204   $94.52   $94.50   $94.50  
  Purchase #3 $25.35   12.186%   $28.4392   $28.44   $28.45   $28.40  
  Purchase #4 $230.40   5.137%   $242.2356   $242.24   $242.25   $242.20  
  Purchase #5 $61.62   6.457%   $65.5988   $65.60   $65.60   $65.60  
  Purchase #6 $240.95   12.392%   $270.8085   $270.81   $270.80   $270.80  
  Purchase #7 $86.90   6.608%   $92.6424   $92.64   $92.65   $92.60  
  7 purchase totals = $878.44       $961.4890   $961.49   $961.50   $961.30