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 $194.60   12.197%   $218.3354   $218.34   $218.35   $218.30  
  Purchase #2 $95.27   9.724%   $104.5341   $104.53   $104.55   $104.50  
  Purchase #3 $238.63   10.438%   $263.5382   $263.54   $263.55   $263.50  
  Purchase #4 $60.80   3.326%   $62.8222   $62.82   $62.80   $62.80  
  Purchase #5 $243.65   11.382%   $271.3822   $271.38   $271.40   $271.40  
  Purchase #6 $238.45   12.446%   $268.1275   $268.13   $268.15   $268.10  
  Purchase #7 $175.56   3.236%   $181.2411   $181.24   $181.25   $181.20  
  7 purchase totals = $1,246.96       $1,369.9807   $1,369.98   $1,370.05   $1,369.80