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 $115.48   5.310%   $121.612   $121.61   $121.60   $121.60  
  Purchase #2 $92.65   3.333%   $95.738   $95.74   $95.75   $95.70  
  Purchase #3 $178.64   8.366%   $193.585   $193.59   $193.60   $193.60  
  Purchase #4 $223.97   8.776%   $243.6256   $243.63   $243.65   $243.60  
  Purchase #5 $98.33   11.143%   $109.2869   $109.29   $109.30   $109.30  
  Purchase #6 $216.40   13.474%   $245.5577   $245.56   $245.55   $245.60  
  Purchase #7 $68.73   7.837%   $74.1164   $74.12   $74.10   $74.10  
  7 purchase totals = $994.20       $1,083.5216   $1,083.54   $1,083.55   $1,083.50