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 $65.28   6.770%   $69.6995   $69.70   $69.70   $69.70  
  Purchase #2 $228.53   6.430%   $243.2245   $243.22   $243.20   $243.20  
  Purchase #3 $147.87   5.359%   $155.7944   $155.79   $155.80   $155.80  
  Purchase #4 $243.25   5.674%   $257.052   $257.05   $257.05   $257.10  
  Purchase #5 $242.78   13.379%   $275.2615   $275.26   $275.25   $275.30  
  Purchase #6 $219.78   6.195%   $233.3954   $233.40   $233.40   $233.40  
  Purchase #7 $135.72   5.802%   $143.5945   $143.59   $143.60   $143.60  
  7 purchase totals = $1,283.21       $1,378.0218   $1,378.01   $1,378.00   $1,378.10