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 $156.46   12.211%   $175.5653   $175.57   $175.55   $175.60  
  Purchase #2 $248.50   8.116%   $268.6683   $268.67   $268.65   $268.70  
  Purchase #3 $62.65   12.721%   $70.6197   $70.62   $70.60   $70.60  
  Purchase #4 $241.36   9.417%   $264.0889   $264.09   $264.10   $264.10  
  Purchase #5 $118.98   8.740%   $129.3789   $129.38   $129.40   $129.40  
  Purchase #6 $101.73   10.795%   $112.7118   $112.71   $112.70   $112.70  
  Purchase #7 $191.42   10.340%   $211.2128   $211.21   $211.20   $211.20  
  7 purchase totals = $1,121.10       $1,232.2457   $1,232.25   $1,232.20   $1,232.30