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 $68.69   9.587%   $75.2753   $75.28   $75.30   $75.30  
  Purchase #2 $218.26   12.414%   $245.3548   $245.35   $245.35   $245.40  
  Purchase #3 $192.32   5.200%   $202.3206   $202.32   $202.30   $202.30  
  Purchase #4 $211.82   12.780%   $238.8906   $238.89   $238.90   $238.90  
  Purchase #5 $106.99   8.498%   $116.082   $116.08   $116.10   $116.10  
  Purchase #6 $232.86   11.625%   $259.93   $259.93   $259.95   $259.90  
  Purchase #7 $160.57   4.649%   $168.0349   $168.03   $168.05   $168.00  
  7 purchase totals = $1,191.51       $1,305.8882   $1,305.88   $1,305.95   $1,305.90