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 $54.46   12.124%   $61.0627   $61.06   $61.05   $61.10  
  Purchase #2 $105.46   13.709%   $119.9175   $119.92   $119.90   $119.90  
  Purchase #3 $191.57   11.235%   $213.0929   $213.09   $213.10   $213.10  
  Purchase #4 $51.47   9.359%   $56.2871   $56.29   $56.30   $56.30  
  Purchase #5 $116.40   3.357%   $120.3075   $120.31   $120.30   $120.30  
  Purchase #6 $70.67   6.394%   $75.1886   $75.19   $75.20   $75.20  
  Purchase #7 $215.41   5.297%   $226.8203   $226.82   $226.80   $226.80  
  7 purchase totals = $805.44       $872.6766   $872.68   $872.65   $872.70