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 $53.32   5.761%   $56.3918   $56.39   $56.40   $56.40  
  Purchase #2 $241.98   11.867%   $270.6958   $270.70   $270.70   $270.70  
  Purchase #3 $76.55   7.455%   $82.2568   $82.26   $82.25   $82.30  
  Purchase #4 $22.46   8.185%   $24.2984   $24.30   $24.30   $24.30  
  Purchase #5 $41.43   6.587%   $44.159   $44.16   $44.15   $44.20  
  Purchase #6 $120.41   12.318%   $135.2421   $135.24   $135.25   $135.20  
  Purchase #7 $108.37   3.346%   $111.9961   $112.00   $112.00   $112.00  
  7 purchase totals = $664.52       $725.0400   $725.05   $725.05   $725.10