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 $63.40   12.613%   $71.3966   $71.40   $71.40   $71.40  
  Purchase #2 $98.73   3.290%   $101.9782   $101.98   $102.00   $102.00  
  Purchase #3 $184.39   4.135%   $192.0145   $192.01   $192.00   $192.00  
  Purchase #4 $191.38   11.411%   $213.2184   $213.22   $213.20   $213.20  
  Purchase #5 $33.79   10.712%   $37.4096   $37.41   $37.40   $37.40  
  Purchase #6 $242.28   7.396%   $260.199   $260.20   $260.20   $260.20  
  Purchase #7 $152.82   11.595%   $170.5395   $170.54   $170.55   $170.50  
  7 purchase totals = $966.79       $1,046.7558   $1,046.76   $1,046.75   $1,046.70