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 $83.43   10.329%   $92.0475   $92.05   $92.05   $92.00  
  Purchase #2 $25.98   3.831%   $26.9753   $26.98   $27.00   $27.00  
  Purchase #3 $45.53   3.416%   $47.0853   $47.09   $47.10   $47.10  
  Purchase #4 $42.54   4.388%   $44.4067   $44.41   $44.40   $44.40  
  Purchase #5 $154.75   3.547%   $160.239   $160.24   $160.25   $160.20  
  Purchase #6 $191.86   6.162%   $203.6824   $203.68   $203.70   $203.70  
  Purchase #7 $17.75   7.106%   $19.0113   $19.01   $19.00   $19.00  
  7 purchase totals = $561.84       $593.4475   $593.46   $593.50   $593.40