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 $153.30   4.500%   $160.1985   $160.20   $160.20   $160.20  
  Purchase #2 $193.83   12.512%   $218.082   $218.08   $218.10   $218.10  
  Purchase #3 $221.73   10.150%   $244.2356   $244.24   $244.25   $244.20  
  Purchase #4 $16.75   11.821%   $18.73   $18.73   $18.75   $18.70  
  Purchase #5 $28.56   3.574%   $29.5807   $29.58   $29.60   $29.60  
  Purchase #6 $143.64   5.336%   $151.3046   $151.30   $151.30   $151.30  
  Purchase #7 $78.60   12.214%   $88.2002   $88.20   $88.20   $88.20  
  7 purchase totals = $836.41       $910.3316   $910.33   $910.40   $910.30