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 $138.92   10.532%   $153.5511   $153.55   $153.55   $153.60  
  Purchase #2 $241.85   13.112%   $273.5614   $273.56   $273.55   $273.60  
  Purchase #3 $107.59   4.217%   $112.1271   $112.13   $112.15   $112.10  
  Purchase #4 $85.52   11.356%   $95.2317   $95.23   $95.25   $95.20  
  Purchase #5 $125.25   3.870%   $130.0972   $130.10   $130.10   $130.10  
  Purchase #6 $229.62   5.792%   $242.9196   $242.92   $242.90   $242.90  
  Purchase #7 $248.86   4.412%   $259.8397   $259.84   $259.85   $259.80  
  7 purchase totals = $1,177.61       $1,267.3278   $1,267.33   $1,267.35   $1,267.30