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 $60.72   9.741%   $66.6347   $66.63   $66.65   $66.60  
  Purchase #2 $151.80   9.837%   $166.7326   $166.73   $166.75   $166.70  
  Purchase #3 $218.37   7.573%   $234.9072   $234.91   $234.90   $234.90  
  Purchase #4 $230.90   5.283%   $243.0984   $243.10   $243.10   $243.10  
  Purchase #5 $166.85   5.611%   $176.212   $176.21   $176.20   $176.20  
  Purchase #6 $120.84   4.686%   $126.5026   $126.50   $126.50   $126.50  
  Purchase #7 $146.98   8.144%   $158.9501   $158.95   $158.95   $159.00  
  7 purchase totals = $1,096.46       $1,173.0376   $1,173.03   $1,173.05   $1,173.00