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 $28.68   13.852%   $32.6528   $32.65   $32.65   $32.70  
  Purchase #2 $241.74   4.548%   $252.7343   $252.73   $252.75   $252.70  
  Purchase #3 $52.53   4.336%   $54.8077   $54.81   $54.80   $54.80  
  Purchase #4 $39.91   6.454%   $42.4858   $42.49   $42.50   $42.50  
  Purchase #5 $173.74   5.676%   $183.6015   $183.60   $183.60   $183.60  
  Purchase #6 $197.93   3.516%   $204.8892   $204.89   $204.90   $204.90  
  Purchase #7 $94.99   12.402%   $106.7707   $106.77   $106.75   $106.80  
  7 purchase totals = $829.52       $877.9420   $877.94   $877.95   $878.00