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 $204.85   11.218%   $227.8301   $227.83   $227.85   $227.80  
  Purchase #2 $62.53   12.248%   $70.1887   $70.19   $70.20   $70.20  
  Purchase #3 $182.31   11.818%   $203.8554   $203.86   $203.85   $203.90  
  Purchase #4 $86.88   6.451%   $92.4846   $92.48   $92.50   $92.50  
  Purchase #5 $232.34   11.225%   $258.4202   $258.42   $258.40   $258.40  
  Purchase #6 $83.27   13.520%   $94.5281   $94.53   $94.55   $94.50  
  Purchase #7 $27.96   13.438%   $31.7173   $31.72   $31.70   $31.70  
  7 purchase totals = $880.14       $979.0244   $979.03   $979.05   $979.00