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 $59.68   6.436%   $63.521   $63.52   $63.50   $63.50  
  Purchase #2 $198.51   6.155%   $210.7283   $210.73   $210.75   $210.70  
  Purchase #3 $60.76   9.772%   $66.6975   $66.70   $66.70   $66.70  
  Purchase #4 $241.59   4.203%   $251.744   $251.74   $251.75   $251.70  
  Purchase #5 $149.59   8.306%   $162.0149   $162.01   $162.00   $162.00  
  Purchase #6 $14.39   4.680%   $15.0635   $15.06   $15.05   $15.10  
  Purchase #7 $101.31   10.238%   $111.6821   $111.68   $111.70   $111.70  
  7 purchase totals = $825.83       $881.4513   $881.44   $881.45   $881.40