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 $83.46   10.818%   $92.4887   $92.49   $92.50   $92.50  
  Purchase #2 $110.48   8.769%   $120.168   $120.17   $120.15   $120.20  
  Purchase #3 $23.41   5.368%   $24.6666   $24.67   $24.65   $24.70  
  Purchase #4 $167.67   4.570%   $175.3325   $175.33   $175.35   $175.30  
  Purchase #5 $156.83   4.378%   $163.696   $163.70   $163.70   $163.70  
  Purchase #6 $187.86   11.745%   $209.9242   $209.92   $209.90   $209.90  
  Purchase #7 $94.37   7.446%   $101.3968   $101.40   $101.40   $101.40  
  7 purchase totals = $824.08       $887.6728   $887.68   $887.65   $887.70