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 $247.85   11.205%   $275.6216   $275.62   $275.60   $275.60  
  Purchase #2 $6.71   13.659%   $7.6265   $7.63   $7.65   $7.60  
  Purchase #3 $128.78   13.138%   $145.6991   $145.70   $145.70   $145.70  
  Purchase #4 $90.68   11.329%   $100.9531   $100.95   $100.95   $101.00  
  Purchase #5 $201.72   12.323%   $226.578   $226.58   $226.60   $226.60  
  Purchase #6 $244.44   8.761%   $265.8554   $265.86   $265.85   $265.90  
  Purchase #7 $41.99   6.661%   $44.787   $44.79   $44.80   $44.80  
  7 purchase totals = $962.17       $1,067.1207   $1,067.13   $1,067.15   $1,067.20