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 $214.70   12.583%   $241.7157   $241.72   $241.70   $241.70  
  Purchase #2 $218.97   5.333%   $230.6477   $230.65   $230.65   $230.60  
  Purchase #3 $70.56   6.466%   $75.1224   $75.12   $75.10   $75.10  
  Purchase #4 $55.38   9.213%   $60.4822   $60.48   $60.50   $60.50  
  Purchase #5 $121.28   5.752%   $128.256   $128.26   $128.25   $128.30  
  Purchase #6 $62.65   3.692%   $64.963   $64.96   $64.95   $65.00  
  Purchase #7 $148.59   12.256%   $166.8012   $166.80   $166.80   $166.80  
  7 purchase totals = $892.13       $967.9882   $967.99   $967.95   $968.00