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 $192.71   13.648%   $219.0111   $219.01   $219.00   $219.00  
  Purchase #2 $239.78   12.501%   $269.7549   $269.75   $269.75   $269.80  
  Purchase #3 $149.31   8.547%   $162.0715   $162.07   $162.05   $162.10  
  Purchase #4 $186.75   5.653%   $197.307   $197.31   $197.30   $197.30  
  Purchase #5 $45.43   5.610%   $47.9786   $47.98   $48.00   $48.00  
  Purchase #6 $149.76   11.258%   $166.62   $166.62   $166.60   $166.60  
  Purchase #7 $145.93   8.529%   $158.3764   $158.38   $158.40   $158.40  
  7 purchase totals = $1,109.67       $1,221.1195   $1,221.12   $1,221.10   $1,221.20