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 $219.95   10.502%   $243.0491   $243.05   $243.05   $243.00  
  Purchase #2 $138.55   11.186%   $154.0482   $154.05   $154.05   $154.00  
  Purchase #3 $120.61   3.277%   $124.5624   $124.56   $124.55   $124.60  
  Purchase #4 $30.60   12.483%   $34.4198   $34.42   $34.40   $34.40  
  Purchase #5 $174.64   6.812%   $186.5365   $186.54   $186.55   $186.50  
  Purchase #6 $87.91   4.803%   $92.1323   $92.13   $92.15   $92.10  
  Purchase #7 $175.84   4.747%   $184.1871   $184.19   $184.20   $184.20  
  7 purchase totals = $948.10       $1,018.9354   $1,018.94   $1,018.95   $1,018.80