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 $180.90   8.149%   $195.6415   $195.64   $195.65   $195.60  
  Purchase #2 $242.78   11.467%   $270.6196   $270.62   $270.60   $270.60  
  Purchase #3 $34.59   8.866%   $37.6567   $37.66   $37.65   $37.70  
  Purchase #4 $232.91   7.865%   $251.2284   $251.23   $251.25   $251.20  
  Purchase #5 $156.85   9.556%   $171.8386   $171.84   $171.85   $171.80  
  Purchase #6 $163.71   11.761%   $182.9639   $182.96   $182.95   $183.00  
  Purchase #7 $193.42   10.532%   $213.791   $213.79   $213.80   $213.80  
  7 purchase totals = $1,205.16       $1,323.7397   $1,323.74   $1,323.75   $1,323.70