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 $239.69   11.526%   $267.3167   $267.32   $267.30   $267.30  
  Purchase #2 $149.87   11.707%   $167.4153   $167.42   $167.40   $167.40  
  Purchase #3 $137.32   12.490%   $154.4713   $154.47   $154.45   $154.50  
  Purchase #4 $235.62   13.350%   $267.0753   $267.08   $267.10   $267.10  
  Purchase #5 $55.37   13.520%   $62.856   $62.86   $62.85   $62.90  
  Purchase #6 $228.93   5.547%   $241.6287   $241.63   $241.65   $241.60  
  Purchase #7 $95.53   12.494%   $107.4655   $107.47   $107.45   $107.50  
  7 purchase totals = $1,142.33       $1,268.2288   $1,268.25   $1,268.20   $1,268.30