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 $87.89   6.729%   $93.8041   $93.80   $93.80   $93.80  
  Purchase #2 $171.25   11.870%   $191.5774   $191.58   $191.60   $191.60  
  Purchase #3 $9.81   9.561%   $10.7479   $10.75   $10.75   $10.70  
  Purchase #4 $236.56   13.852%   $269.3283   $269.33   $269.35   $269.30  
  Purchase #5 $82.28   4.286%   $85.8065   $85.81   $85.80   $85.80  
  Purchase #6 $201.28   11.794%   $225.019   $225.02   $225.00   $225.00  
  Purchase #7 $176.83   10.115%   $194.7164   $194.72   $194.70   $194.70  
  7 purchase totals = $965.90       $1,070.9996   $1,071.01   $1,071.00   $1,070.90