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 $69.25   8.336%   $75.0227   $75.02   $75.00   $75.00  
  Purchase #2 $24.51   6.129%   $26.0122   $26.01   $26.00   $26.00  
  Purchase #3 $188.74   6.264%   $200.5627   $200.56   $200.55   $200.60  
  Purchase #4 $22.35   3.450%   $23.1211   $23.12   $23.10   $23.10  
  Purchase #5 $118.85   8.663%   $129.146   $129.15   $129.15   $129.10  
  Purchase #6 $91.80   12.252%   $103.0473   $103.05   $103.05   $103.00  
  Purchase #7 $187.53   5.192%   $197.2666   $197.27   $197.25   $197.30  
  7 purchase totals = $703.03       $754.1786   $754.18   $754.10   $754.10