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 $87.67   9.524%   $96.0197   $96.02   $96.00   $96.00  
  Purchase #2 $119.75   3.292%   $123.6922   $123.69   $123.70   $123.70  
  Purchase #3 $135.97   11.635%   $151.7901   $151.79   $151.80   $151.80  
  Purchase #4 $160.93   13.855%   $183.2269   $183.23   $183.25   $183.20  
  Purchase #5 $124.64   9.211%   $136.1206   $136.12   $136.10   $136.10  
  Purchase #6 $205.57   7.663%   $221.3228   $221.32   $221.30   $221.30  
  Purchase #7 $79.75   3.667%   $82.6744   $82.67   $82.65   $82.70  
  7 purchase totals = $914.28       $994.8467   $994.84   $994.80   $994.80