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 $36.47   12.842%   $41.1535   $41.15   $41.15   $41.20  
  Purchase #2 $76.72   10.701%   $84.9298   $84.93   $84.95   $84.90  
  Purchase #3 $5.93   13.123%   $6.7082   $6.71   $6.70   $6.70  
  Purchase #4 $75.89   12.725%   $85.547   $85.55   $85.55   $85.50  
  Purchase #5 $79.70   9.784%   $87.4978   $87.50   $87.50   $87.50  
  Purchase #6 $49.26   6.529%   $52.4762   $52.48   $52.50   $52.50  
  Purchase #7 $6.77   11.762%   $7.5663   $7.57   $7.55   $7.60  
  7 purchase totals = $330.74       $365.8788   $365.89   $365.90   $365.90