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 $142.40   11.849%   $159.273   $159.27   $159.25   $159.30  
  Purchase #2 $24.49   6.263%   $26.0238   $26.02   $26.00   $26.00  
  Purchase #3 $110.27   9.332%   $120.5604   $120.56   $120.55   $120.60  
  Purchase #4 $163.89   10.572%   $181.2165   $181.22   $181.20   $181.20  
  Purchase #5 $29.25   11.551%   $32.6287   $32.63   $32.65   $32.60  
  Purchase #6 $160.73   13.522%   $182.4639   $182.46   $182.45   $182.50  
  Purchase #7 $213.90   12.614%   $240.8813   $240.88   $240.90   $240.90  
  7 purchase totals = $844.93       $943.0476   $943.04   $943.00   $943.10