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 $36.86   4.792%   $38.6263   $38.63   $38.65   $38.60  
  Purchase #2 $33.26   10.432%   $36.7297   $36.73   $36.75   $36.70  
  Purchase #3 $98.55   9.104%   $107.522   $107.52   $107.50   $107.50  
  Purchase #4 $239.94   7.661%   $258.3218   $258.32   $258.30   $258.30  
  Purchase #5 $247.63   7.244%   $265.5683   $265.57   $265.55   $265.60  
  Purchase #6 $160.62   3.117%   $165.6265   $165.63   $165.65   $165.60  
  Purchase #7 $179.78   13.702%   $204.4135   $204.41   $204.40   $204.40  
  7 purchase totals = $996.64       $1,076.8081   $1,076.81   $1,076.80   $1,076.70