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 $54.50   11.627%   $60.8367   $60.84   $60.85   $60.80  
  Purchase #2 $240.68   13.698%   $273.6483   $273.65   $273.65   $273.60  
  Purchase #3 $117.38   12.775%   $132.3753   $132.38   $132.40   $132.40  
  Purchase #4 $97.57   10.540%   $107.8539   $107.85   $107.85   $107.90  
  Purchase #5 $54.74   9.113%   $59.7285   $59.73   $59.75   $59.70  
  Purchase #6 $210.79   10.314%   $232.5309   $232.53   $232.55   $232.50  
  Purchase #7 $154.52   7.649%   $166.3392   $166.34   $166.35   $166.30  
  7 purchase totals = $930.18       $1,033.3128   $1,033.32   $1,033.40   $1,033.20