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 $202.51   9.626%   $222.0036   $222.00   $222.00   $222.00  
  Purchase #2 $173.89   10.160%   $191.5572   $191.56   $191.55   $191.60  
  Purchase #3 $69.30   5.532%   $73.1337   $73.13   $73.15   $73.10  
  Purchase #4 $191.97   12.379%   $215.734   $215.73   $215.75   $215.70  
  Purchase #5 $147.37   13.671%   $167.517   $167.52   $167.50   $167.50  
  Purchase #6 $206.74   12.427%   $232.4316   $232.43   $232.45   $232.40  
  Purchase #7 $86.94   10.569%   $96.1287   $96.13   $96.15   $96.10  
  7 purchase totals = $1,078.72       $1,198.5058   $1,198.50   $1,198.55   $1,198.40