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 $236.27   8.215%   $255.6796   $255.68   $255.70   $255.70  
  Purchase #2 $60.88   3.861%   $63.2306   $63.23   $63.25   $63.20  
  Purchase #3 $230.51   9.666%   $252.7911   $252.79   $252.80   $252.80  
  Purchase #4 $87.54   4.684%   $91.6404   $91.64   $91.65   $91.60  
  Purchase #5 $223.86   9.631%   $245.42   $245.42   $245.40   $245.40  
  Purchase #6 $52.74   7.253%   $56.5652   $56.57   $56.55   $56.60  
  Purchase #7 $149.48   4.292%   $155.8957   $155.90   $155.90   $155.90  
  7 purchase totals = $1,041.28       $1,121.2226   $1,121.23   $1,121.25   $1,121.20