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 $189.68   6.672%   $202.3354   $202.34   $202.35   $202.30  
  Purchase #2 $238.61   11.801%   $266.7684   $266.77   $266.75   $266.80  
  Purchase #3 $41.80   11.426%   $46.5761   $46.58   $46.60   $46.60  
  Purchase #4 $69.89   8.359%   $75.7321   $75.73   $75.75   $75.70  
  Purchase #5 $86.63   5.856%   $91.7031   $91.70   $91.70   $91.70  
  Purchase #6 $198.47   3.714%   $205.8412   $205.84   $205.85   $205.80  
  Purchase #7 $225.96   3.106%   $232.9783   $232.98   $233.00   $233.00  
  7 purchase totals = $1,051.04       $1,121.9346   $1,121.94   $1,122.00   $1,121.90