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 $64.91   12.212%   $72.8368   $72.84   $72.85   $72.80  
  Purchase #2 $116.59   3.333%   $120.4759   $120.48   $120.50   $120.50  
  Purchase #3 $97.93   5.192%   $103.0145   $103.01   $103.00   $103.00  
  Purchase #4 $49.62   10.829%   $54.9933   $54.99   $55.00   $55.00  
  Purchase #5 $116.35   6.679%   $124.121   $124.12   $124.10   $124.10  
  Purchase #6 $201.29   6.735%   $214.8469   $214.85   $214.85   $214.80  
  Purchase #7 $37.29   11.255%   $41.487   $41.49   $41.50   $41.50  
  7 purchase totals = $683.98       $731.7754   $731.78   $731.80   $731.70