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 $91.96   3.130%   $94.8383   $94.84   $94.85   $94.80  
  Purchase #2 $117.25   6.752%   $125.1667   $125.17   $125.15   $125.20  
  Purchase #3 $165.59   3.255%   $170.98   $170.98   $171.00   $171.00  
  Purchase #4 $115.99   4.731%   $121.4775   $121.48   $121.50   $121.50  
  Purchase #5 $73.82   10.363%   $81.47   $81.47   $81.45   $81.50  
  Purchase #6 $186.28   9.768%   $204.4758   $204.48   $204.50   $204.50  
  Purchase #7 $156.63   13.690%   $178.0726   $178.07   $178.05   $178.10  
  7 purchase totals = $907.52       $976.4809   $976.49   $976.50   $976.60