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 $202.63   9.202%   $221.276   $221.28   $221.30   $221.30  
  Purchase #2 $80.57   3.459%   $83.3569   $83.36   $83.35   $83.40  
  Purchase #3 $63.59   7.565%   $68.4006   $68.40   $68.40   $68.40  
  Purchase #4 $33.30   6.374%   $35.4225   $35.42   $35.40   $35.40  
  Purchase #5 $17.42   6.505%   $18.5532   $18.55   $18.55   $18.60  
  Purchase #6 $243.99   9.825%   $267.962   $267.96   $267.95   $268.00  
  Purchase #7 $55.75   6.346%   $59.2879   $59.29   $59.30   $59.30  
  7 purchase totals = $697.25       $754.2591   $754.26   $754.25   $754.40