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 $80.67   6.562%   $85.9636   $85.96   $85.95   $86.00  
  Purchase #2 $53.99   10.832%   $59.8382   $59.84   $59.85   $59.80  
  Purchase #3 $91.62   13.304%   $103.8091   $103.81   $103.80   $103.80  
  Purchase #4 $123.65   9.748%   $135.7034   $135.70   $135.70   $135.70  
  Purchase #5 $180.26   7.695%   $194.131   $194.13   $194.15   $194.10  
  Purchase #6 $102.75   4.648%   $107.5258   $107.53   $107.55   $107.50  
  Purchase #7 $124.35   8.640%   $135.0938   $135.09   $135.10   $135.10  
  7 purchase totals = $757.29       $822.0649   $822.06   $822.10   $822.00