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 $215.86   4.231%   $224.993   $224.99   $225.00   $225.00  
  Purchase #2 $120.40   11.248%   $133.9426   $133.94   $133.95   $133.90  
  Purchase #3 $185.87   4.215%   $193.7044   $193.70   $193.70   $193.70  
  Purchase #4 $229.87   6.827%   $245.5632   $245.56   $245.55   $245.60  
  Purchase #5 $193.63   9.819%   $212.6425   $212.64   $212.65   $212.60  
  Purchase #6 $101.86   6.133%   $108.1071   $108.11   $108.10   $108.10  
  Purchase #7 $119.85   9.613%   $131.3712   $131.37   $131.35   $131.40  
  7 purchase totals = $1,167.34       $1,250.3240   $1,250.31   $1,250.30   $1,250.30