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 $53.49   10.259%   $58.9775   $58.98   $59.00   $59.00  
  Purchase #2 $184.41   4.361%   $192.4521   $192.45   $192.45   $192.50  
  Purchase #3 $23.38   12.792%   $26.3708   $26.37   $26.35   $26.40  
  Purchase #4 $115.97   7.843%   $125.0655   $125.07   $125.05   $125.10  
  Purchase #5 $9.54   10.765%   $10.567   $10.57   $10.55   $10.60  
  Purchase #6 $192.83   13.861%   $219.5582   $219.56   $219.55   $219.60  
  Purchase #7 $117.70   4.740%   $123.279   $123.28   $123.30   $123.30  
  7 purchase totals = $697.32       $756.2701   $756.28   $756.25   $756.50