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 $118.40   11.446%   $131.9521   $131.95   $131.95   $132.00  
  Purchase #2 $156.84   5.362%   $165.2498   $165.25   $165.25   $165.20  
  Purchase #3 $187.93   10.521%   $207.7021   $207.70   $207.70   $207.70  
  Purchase #4 $26.47   11.752%   $29.5808   $29.58   $29.60   $29.60  
  Purchase #5 $71.63   4.439%   $74.8097   $74.81   $74.80   $74.80  
  Purchase #6 $233.30   13.532%   $264.8702   $264.87   $264.85   $264.90  
  Purchase #7 $141.79   10.135%   $156.1604   $156.16   $156.15   $156.20  
  7 purchase totals = $936.36       $1,030.3251   $1,030.32   $1,030.30   $1,030.40