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 $126.89   4.399%   $132.4719   $132.47   $132.45   $132.50  
  Purchase #2 $192.31   6.551%   $204.9082   $204.91   $204.90   $204.90  
  Purchase #3 $235.30   13.154%   $266.2514   $266.25   $266.25   $266.30  
  Purchase #4 $193.62   13.523%   $219.8032   $219.80   $219.80   $219.80  
  Purchase #5 $94.73   4.120%   $98.6329   $98.63   $98.65   $98.60  
  Purchase #6 $199.84   6.438%   $212.7057   $212.71   $212.70   $212.70  
  Purchase #7 $223.99   4.436%   $233.9262   $233.93   $233.95   $233.90  
  7 purchase totals = $1,266.68       $1,368.6995   $1,368.70   $1,368.70   $1,368.70