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 $235.72   7.742%   $253.9694   $253.97   $253.95   $254.00  
  Purchase #2 $65.48   11.109%   $72.7542   $72.75   $72.75   $72.80  
  Purchase #3 $23.29   10.569%   $25.7515   $25.75   $25.75   $25.80  
  Purchase #4 $184.39   6.806%   $196.9396   $196.94   $196.95   $196.90  
  Purchase #5 $240.71   11.261%   $267.8164   $267.82   $267.80   $267.80  
  Purchase #6 $156.40   11.113%   $173.7807   $173.78   $173.80   $173.80  
  Purchase #7 $197.77   7.587%   $212.7748   $212.77   $212.75   $212.80  
  7 purchase totals = $1,103.76       $1,203.7866   $1,203.78   $1,203.75   $1,203.90