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 $185.55   9.261%   $202.7338   $202.73   $202.75   $202.70  
  Purchase #2 $230.31   7.102%   $246.6666   $246.67   $246.65   $246.70  
  Purchase #3 $94.76   12.754%   $106.8457   $106.85   $106.85   $106.80  
  Purchase #4 $166.99   5.216%   $175.7002   $175.70   $175.70   $175.70  
  Purchase #5 $68.73   8.701%   $74.7102   $74.71   $74.70   $74.70  
  Purchase #6 $13.72   9.565%   $15.0323   $15.03   $15.05   $15.00  
  Purchase #7 $133.29   6.671%   $142.1818   $142.18   $142.20   $142.20  
  7 purchase totals = $893.35       $963.8706   $963.87   $963.90   $963.80