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 $108.63   4.192%   $113.1838   $113.18   $113.20   $113.20  
  Purchase #2 $85.66   7.524%   $92.1051   $92.11   $92.10   $92.10  
  Purchase #3 $106.48   10.787%   $117.966   $117.97   $117.95   $118.00  
  Purchase #4 $24.57   12.488%   $27.6383   $27.64   $27.65   $27.60  
  Purchase #5 $233.55   4.435%   $243.9079   $243.91   $243.90   $243.90  
  Purchase #6 $152.91   10.462%   $168.9074   $168.91   $168.90   $168.90  
  Purchase #7 $241.59   7.620%   $259.9992   $260.00   $260.00   $260.00  
  7 purchase totals = $953.39       $1,023.7077   $1,023.72   $1,023.70   $1,023.70