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 $230.93   8.589%   $250.7646   $250.76   $250.75   $250.80  
  Purchase #2 $83.79   13.534%   $95.1301   $95.13   $95.15   $95.10  
  Purchase #3 $242.98   4.341%   $253.5278   $253.53   $253.55   $253.50  
  Purchase #4 $175.53   9.560%   $192.3107   $192.31   $192.30   $192.30  
  Purchase #5 $207.80   12.337%   $233.4363   $233.44   $233.45   $233.40  
  Purchase #6 $240.62   4.294%   $250.9522   $250.95   $250.95   $251.00  
  Purchase #7 $167.52   11.409%   $186.6324   $186.63   $186.65   $186.60  
  7 purchase totals = $1,349.17       $1,462.7541   $1,462.75   $1,462.80   $1,462.70