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 $173.81   13.708%   $197.6359   $197.64   $197.65   $197.60  
  Purchase #2 $147.68   6.325%   $157.0208   $157.02   $157.00   $157.00  
  Purchase #3 $17.35   12.334%   $19.4899   $19.49   $19.50   $19.50  
  Purchase #4 $26.59   9.213%   $29.0397   $29.04   $29.05   $29.00  
  Purchase #5 $210.90   10.865%   $233.8143   $233.81   $233.80   $233.80  
  Purchase #6 $11.74   3.799%   $12.186   $12.19   $12.20   $12.20  
  Purchase #7 $131.44   13.469%   $149.1437   $149.14   $149.15   $149.10  
  7 purchase totals = $719.51       $798.3303   $798.33   $798.35   $798.20