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 $168.29   9.136%   $183.665   $183.67   $183.65   $183.70  
  Purchase #2 $179.49   12.772%   $202.4145   $202.41   $202.40   $202.40  
  Purchase #3 $49.60   13.181%   $56.1378   $56.14   $56.15   $56.10  
  Purchase #4 $227.72   13.725%   $258.9746   $258.97   $258.95   $259.00  
  Purchase #5 $226.56   5.304%   $238.5767   $238.58   $238.60   $238.60  
  Purchase #6 $154.61   7.321%   $165.929   $165.93   $165.95   $165.90  
  Purchase #7 $54.65   13.666%   $62.1185   $62.12   $62.10   $62.10  
  7 purchase totals = $1,060.92       $1,167.8161   $1,167.82   $1,167.80   $1,167.80