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 $246.89   11.686%   $275.7416   $275.74   $275.75   $275.70  
  Purchase #2 $5.26   3.438%   $5.4408   $5.44   $5.45   $5.40  
  Purchase #3 $78.69   6.267%   $83.6215   $83.62   $83.60   $83.60  
  Purchase #4 $75.44   10.593%   $83.4314   $83.43   $83.45   $83.40  
  Purchase #5 $136.37   11.331%   $151.8221   $151.82   $151.80   $151.80  
  Purchase #6 $196.97   4.512%   $205.8573   $205.86   $205.85   $205.90  
  Purchase #7 $124.70   8.233%   $134.9666   $134.97   $134.95   $135.00  
  7 purchase totals = $864.32       $940.8813   $940.88   $940.85   $940.80