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 $241.53   11.197%   $268.5741   $268.57   $268.55   $268.60  
  Purchase #2 $241.76   13.693%   $274.8642   $274.86   $274.85   $274.90  
  Purchase #3 $8.44   6.112%   $8.9559   $8.96   $8.95   $9.00  
  Purchase #4 $186.26   13.551%   $211.5001   $211.50   $211.50   $211.50  
  Purchase #5 $90.56   5.554%   $95.5897   $95.59   $95.60   $95.60  
  Purchase #6 $90.64   6.145%   $96.2098   $96.21   $96.20   $96.20  
  Purchase #7 $197.74   7.489%   $212.5487   $212.55   $212.55   $212.50  
  7 purchase totals = $1,056.93       $1,168.2425   $1,168.24   $1,168.20   $1,168.30