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 $74.73   10.841%   $82.8315   $82.83   $82.85   $82.80  
  Purchase #2 $201.98   13.847%   $229.9482   $229.95   $229.95   $229.90  
  Purchase #3 $202.62   5.118%   $212.9901   $212.99   $213.00   $213.00  
  Purchase #4 $132.25   3.108%   $136.3603   $136.36   $136.35   $136.40  
  Purchase #5 $195.83   6.760%   $209.0681   $209.07   $209.05   $209.10  
  Purchase #6 $116.84   8.454%   $126.7177   $126.72   $126.70   $126.70  
  Purchase #7 $51.28   12.609%   $57.7459   $57.75   $57.75   $57.70  
  7 purchase totals = $975.53       $1,055.6618   $1,055.67   $1,055.65   $1,055.60