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 $212.46   10.763%   $235.3271   $235.33   $235.35   $235.30  
  Purchase #2 $231.51   12.134%   $259.6014   $259.60   $259.60   $259.60  
  Purchase #3 $159.48   12.551%   $179.4963   $179.50   $179.50   $179.50  
  Purchase #4 $31.30   12.639%   $35.256   $35.26   $35.25   $35.30  
  Purchase #5 $10.91   8.114%   $11.7952   $11.80   $11.80   $11.80  
  Purchase #6 $120.66   8.620%   $131.0609   $131.06   $131.05   $131.10  
  Purchase #7 $134.96   4.303%   $140.7673   $140.77   $140.75   $140.80  
  7 purchase totals = $901.28       $993.3042   $993.32   $993.30   $993.40