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 $82.86   11.424%   $92.3259   $92.33   $92.35   $92.30  
  Purchase #2 $211.82   3.699%   $219.6552   $219.66   $219.65   $219.70  
  Purchase #3 $84.35   8.691%   $91.6809   $91.68   $91.70   $91.70  
  Purchase #4 $103.34   8.589%   $112.2159   $112.22   $112.20   $112.20  
  Purchase #5 $60.68   9.490%   $66.4385   $66.44   $66.45   $66.40  
  Purchase #6 $167.56   5.509%   $176.7909   $176.79   $176.80   $176.80  
  Purchase #7 $105.60   3.158%   $108.9348   $108.93   $108.95   $108.90  
  7 purchase totals = $816.21       $868.0421   $868.05   $868.10   $868.00