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 $237.77   12.147%   $266.6519   $266.65   $266.65   $266.70  
  Purchase #2 $94.50   12.511%   $106.3229   $106.32   $106.30   $106.30  
  Purchase #3 $182.47   5.754%   $192.9693   $192.97   $192.95   $193.00  
  Purchase #4 $109.29   5.825%   $115.6561   $115.66   $115.65   $115.70  
  Purchase #5 $237.79   7.862%   $256.485   $256.49   $256.50   $256.50  
  Purchase #6 $38.41   6.603%   $40.9462   $40.95   $40.95   $40.90  
  Purchase #7 $247.42   4.200%   $257.8116   $257.81   $257.80   $257.80  
  7 purchase totals = $1,147.65       $1,236.8430   $1,236.85   $1,236.80   $1,236.90