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 $32.88   12.398%   $36.9565   $36.96   $36.95   $37.00  
  Purchase #2 $243.95   5.374%   $257.0599   $257.06   $257.05   $257.10  
  Purchase #3 $195.84   8.181%   $211.8617   $211.86   $211.85   $211.90  
  Purchase #4 $243.66   12.675%   $274.5439   $274.54   $274.55   $274.50  
  Purchase #5 $198.86   12.690%   $224.0953   $224.10   $224.10   $224.10  
  Purchase #6 $217.60   7.328%   $233.5457   $233.55   $233.55   $233.50  
  Purchase #7 $108.86   13.565%   $123.6269   $123.63   $123.65   $123.60  
  7 purchase totals = $1,241.65       $1,361.6899   $1,361.70   $1,361.70   $1,361.70