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 $184.27   12.658%   $207.5949   $207.59   $207.60   $207.60  
  Purchase #2 $91.29   3.300%   $94.3026   $94.30   $94.30   $94.30  
  Purchase #3 $46.86   6.304%   $49.8141   $49.81   $49.80   $49.80  
  Purchase #4 $25.49   12.229%   $28.6072   $28.61   $28.60   $28.60  
  Purchase #5 $131.96   7.757%   $142.1961   $142.20   $142.20   $142.20  
  Purchase #6 $180.36   9.713%   $197.8784   $197.88   $197.90   $197.90  
  Purchase #7 $195.91   3.777%   $203.3095   $203.31   $203.30   $203.30  
  7 purchase totals = $856.14       $923.7028   $923.70   $923.70   $923.70