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 $197.78   10.356%   $218.2621   $218.26   $218.25   $218.30  
  Purchase #2 $233.32   4.273%   $243.2898   $243.29   $243.30   $243.30  
  Purchase #3 $231.76   10.492%   $256.0763   $256.08   $256.10   $256.10  
  Purchase #4 $180.99   3.447%   $187.2287   $187.23   $187.25   $187.20  
  Purchase #5 $207.66   11.606%   $231.761   $231.76   $231.75   $231.80  
  Purchase #6 $189.35   9.682%   $207.6829   $207.68   $207.70   $207.70  
  Purchase #7 $83.91   11.359%   $93.4413   $93.44   $93.45   $93.40  
  7 purchase totals = $1,324.77       $1,437.7421   $1,437.74   $1,437.80   $1,437.80