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 $169.73   8.360%   $183.9194   $183.92   $183.90   $183.90  
  Purchase #2 $208.59   11.349%   $232.2629   $232.26   $232.25   $232.30  
  Purchase #3 $161.56   5.618%   $170.6364   $170.64   $170.65   $170.60  
  Purchase #4 $156.76   7.558%   $168.6079   $168.61   $168.60   $168.60  
  Purchase #5 $228.92   6.689%   $244.2325   $244.23   $244.25   $244.20  
  Purchase #6 $106.71   5.747%   $112.8426   $112.84   $112.85   $112.80  
  Purchase #7 $236.47   9.177%   $258.1709   $258.17   $258.15   $258.20  
  7 purchase totals = $1,268.74       $1,370.6726   $1,370.67   $1,370.65   $1,370.60