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 $105.52   12.504%   $118.7142   $118.71   $118.70   $118.70  
  Purchase #2 $26.61   10.162%   $29.3141   $29.31   $29.30   $29.30  
  Purchase #3 $210.48   4.606%   $220.1747   $220.17   $220.15   $220.20  
  Purchase #4 $193.32   5.477%   $203.9081   $203.91   $203.90   $203.90  
  Purchase #5 $247.29   3.624%   $256.2518   $256.25   $256.25   $256.30  
  Purchase #6 $132.27   3.561%   $136.9801   $136.98   $137.00   $137.00  
  Purchase #7 $56.96   3.269%   $58.822   $58.82   $58.80   $58.80  
  7 purchase totals = $972.45       $1,024.1650   $1,024.15   $1,024.10   $1,024.20