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 $233.84   12.235%   $262.4503   $262.45   $262.45   $262.50  
  Purchase #2 $73.93   13.582%   $83.9712   $83.97   $83.95   $84.00  
  Purchase #3 $91.51   13.807%   $104.1448   $104.14   $104.15   $104.10  
  Purchase #4 $60.33   8.712%   $65.5859   $65.59   $65.60   $65.60  
  Purchase #5 $245.87   8.843%   $267.6123   $267.61   $267.60   $267.60  
  Purchase #6 $148.79   13.344%   $168.6445   $168.64   $168.65   $168.60  
  Purchase #7 $167.73   6.256%   $178.2232   $178.22   $178.20   $178.20  
  7 purchase totals = $1,022.00       $1,130.6322   $1,130.62   $1,130.60   $1,130.60