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 $34.56   11.641%   $38.5831   $38.58   $38.60   $38.60  
  Purchase #2 $188.46   3.629%   $195.2992   $195.30   $195.30   $195.30  
  Purchase #3 $43.27   6.562%   $46.1094   $46.11   $46.10   $46.10  
  Purchase #4 $204.71   13.641%   $232.6345   $232.63   $232.65   $232.60  
  Purchase #5 $41.42   3.420%   $42.8366   $42.84   $42.85   $42.80  
  Purchase #6 $233.62   4.773%   $244.7707   $244.77   $244.75   $244.80  
  Purchase #7 $159.96   10.367%   $176.5431   $176.54   $176.55   $176.50  
  7 purchase totals = $906.00       $976.7766   $976.77   $976.80   $976.70