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 $118.58   4.597%   $124.0311   $124.03   $124.05   $124.00  
  Purchase #2 $44.57   8.614%   $48.4093   $48.41   $48.40   $48.40  
  Purchase #3 $127.85   11.636%   $142.7266   $142.73   $142.75   $142.70  
  Purchase #4 $200.75   9.137%   $219.0925   $219.09   $219.10   $219.10  
  Purchase #5 $156.68   7.380%   $168.243   $168.24   $168.25   $168.20  
  Purchase #6 $229.88   11.803%   $257.0127   $257.01   $257.00   $257.00  
  Purchase #7 $57.25   12.440%   $64.3719   $64.37   $64.35   $64.40  
  7 purchase totals = $935.56       $1,023.8871   $1,023.88   $1,023.90   $1,023.80