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 $83.75   9.473%   $91.6836   $91.68   $91.70   $91.70  
  Purchase #2 $195.55   5.500%   $206.3053   $206.31   $206.30   $206.30  
  Purchase #3 $193.89   7.726%   $208.8699   $208.87   $208.85   $208.90  
  Purchase #4 $184.76   3.797%   $191.7753   $191.78   $191.80   $191.80  
  Purchase #5 $133.75   13.226%   $151.4398   $151.44   $151.45   $151.40  
  Purchase #6 $192.51   4.525%   $201.2211   $201.22   $201.20   $201.20  
  Purchase #7 $169.52   8.614%   $184.1225   $184.12   $184.10   $184.10  
  7 purchase totals = $1,153.73       $1,235.4175   $1,235.42   $1,235.40   $1,235.40