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 $69.54   8.748%   $75.6234   $75.62   $75.60   $75.60  
  Purchase #2 $165.78   13.403%   $187.9995   $188.00   $188.00   $188.00  
  Purchase #3 $202.46   6.809%   $216.2455   $216.25   $216.25   $216.20  
  Purchase #4 $150.27   11.483%   $167.5255   $167.53   $167.55   $167.50  
  Purchase #5 $64.77   10.379%   $71.4925   $71.49   $71.50   $71.50  
  Purchase #6 $25.66   9.853%   $28.1883   $28.19   $28.20   $28.20  
  Purchase #7 $18.48   4.765%   $19.3606   $19.36   $19.35   $19.40  
  7 purchase totals = $696.96       $766.4353   $766.44   $766.45   $766.40