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 $72.85   3.123%   $75.1251   $75.13   $75.15   $75.10  
  Purchase #2 $172.88   9.122%   $188.6501   $188.65   $188.65   $188.70  
  Purchase #3 $106.31   9.189%   $116.0788   $116.08   $116.10   $116.10  
  Purchase #4 $98.84   5.606%   $104.381   $104.38   $104.40   $104.40  
  Purchase #5 $223.56   11.736%   $249.797   $249.80   $249.80   $249.80  
  Purchase #6 $191.27   5.215%   $201.2447   $201.24   $201.25   $201.20  
  Purchase #7 $94.30   4.296%   $98.3511   $98.35   $98.35   $98.40  
  7 purchase totals = $960.01       $1,033.6278   $1,033.63   $1,033.70   $1,033.70