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 $240.64   10.824%   $266.6869   $266.69   $266.70   $266.70  
  Purchase #2 $109.58   9.681%   $120.1884   $120.19   $120.20   $120.20  
  Purchase #3 $84.94   11.828%   $94.9867   $94.99   $95.00   $95.00  
  Purchase #4 $208.82   7.252%   $223.9636   $223.96   $223.95   $224.00  
  Purchase #5 $71.84   8.614%   $78.0283   $78.03   $78.05   $78.00  
  Purchase #6 $235.73   7.602%   $253.6502   $253.65   $253.65   $253.70  
  Purchase #7 $179.80   13.591%   $204.2366   $204.24   $204.25   $204.20  
  7 purchase totals = $1,131.35       $1,241.7407   $1,241.75   $1,241.80   $1,241.80