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 $32.96   11.473%   $36.7415   $36.74   $36.75   $36.70  
  Purchase #2 $49.55   13.413%   $56.1961   $56.20   $56.20   $56.20  
  Purchase #3 $86.99   6.478%   $92.6252   $92.63   $92.65   $92.60  
  Purchase #4 $150.25   11.802%   $167.9825   $167.98   $168.00   $168.00  
  Purchase #5 $18.25   4.326%   $19.0395   $19.04   $19.05   $19.00  
  Purchase #6 $69.56   8.192%   $75.2584   $75.26   $75.25   $75.30  
  Purchase #7 $9.35   9.164%   $10.2068   $10.21   $10.20   $10.20  
  7 purchase totals = $416.91       $458.0500   $458.06   $458.10   $458.00