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 $187.29   7.839%   $201.9717   $201.97   $201.95   $202.00  
  Purchase #2 $226.36   8.592%   $245.8089   $245.81   $245.80   $245.80  
  Purchase #3 $82.81   6.555%   $88.2382   $88.24   $88.25   $88.20  
  Purchase #4 $112.95   12.377%   $126.9298   $126.93   $126.95   $126.90  
  Purchase #5 $239.28   6.265%   $254.2709   $254.27   $254.25   $254.30  
  Purchase #6 $249.77   3.705%   $259.024   $259.02   $259.00   $259.00  
  Purchase #7 $37.42   9.564%   $40.9988   $41.00   $41.00   $41.00  
  7 purchase totals = $1,135.88       $1,217.2423   $1,217.24   $1,217.20   $1,217.20