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 $39.75   10.771%   $44.0315   $44.03   $44.05   $44.00  
  Purchase #2 $201.59   9.399%   $220.5374   $220.54   $220.55   $220.50  
  Purchase #3 $206.86   4.652%   $216.4831   $216.48   $216.50   $216.50  
  Purchase #4 $161.61   6.515%   $172.1389   $172.14   $172.15   $172.10  
  Purchase #5 $63.86   6.343%   $67.9106   $67.91   $67.90   $67.90  
  Purchase #6 $194.87   5.249%   $205.0987   $205.10   $205.10   $205.10  
  Purchase #7 $32.88   3.753%   $34.114   $34.11   $34.10   $34.10  
  7 purchase totals = $901.42       $960.3142   $960.31   $960.35   $960.20