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 $129.90   3.163%   $134.0087   $134.01   $134.00   $134.00  
  Purchase #2 $243.34   5.169%   $255.9182   $255.92   $255.90   $255.90  
  Purchase #3 $188.96   9.245%   $206.4294   $206.43   $206.45   $206.40  
  Purchase #4 $17.69   5.263%   $18.621   $18.62   $18.60   $18.60  
  Purchase #5 $88.67   10.207%   $97.7205   $97.72   $97.70   $97.70  
  Purchase #6 $214.80   4.852%   $225.2221   $225.22   $225.20   $225.20  
  Purchase #7 $207.30   4.383%   $216.386   $216.39   $216.40   $216.40  
  7 purchase totals = $1,090.66       $1,154.3059   $1,154.31   $1,154.25   $1,154.20