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 $166.62   5.812%   $176.304   $176.30   $176.30   $176.30  
  Purchase #2 $39.82   3.112%   $41.0592   $41.06   $41.05   $41.10  
  Purchase #3 $65.88   10.291%   $72.6597   $72.66   $72.65   $72.70  
  Purchase #4 $120.33   8.239%   $130.244   $130.24   $130.25   $130.20  
  Purchase #5 $162.29   8.305%   $175.7682   $175.77   $175.75   $175.80  
  Purchase #6 $8.37   5.130%   $8.7994   $8.80   $8.80   $8.80  
  Purchase #7 $218.52   5.286%   $230.071   $230.07   $230.05   $230.10  
  7 purchase totals = $781.83       $834.9055   $834.90   $834.85   $835.00