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 $49.61   5.803%   $52.4889   $52.49   $52.50   $52.50  
  Purchase #2 $104.37   13.750%   $118.7209   $118.72   $118.70   $118.70  
  Purchase #3 $173.79   5.133%   $182.7106   $182.71   $182.70   $182.70  
  Purchase #4 $209.96   4.625%   $219.6707   $219.67   $219.65   $219.70  
  Purchase #5 $237.97   6.687%   $253.8831   $253.88   $253.90   $253.90  
  Purchase #6 $241.55   9.277%   $263.9586   $263.96   $263.95   $264.00  
  Purchase #7 $163.50   4.853%   $171.4347   $171.43   $171.45   $171.40  
  7 purchase totals = $1,180.75       $1,262.8675   $1,262.86   $1,262.85   $1,262.90