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 $112.76   4.661%   $118.0157   $118.02   $118.00   $118.00  
  Purchase #2 $201.34   8.801%   $219.0599   $219.06   $219.05   $219.10  
  Purchase #3 $143.68   6.848%   $153.5192   $153.52   $153.50   $153.50  
  Purchase #4 $118.70   13.452%   $134.6675   $134.67   $134.65   $134.70  
  Purchase #5 $91.53   10.153%   $100.823   $100.82   $100.80   $100.80  
  Purchase #6 $67.61   12.416%   $76.0045   $76.00   $76.00   $76.00  
  Purchase #7 $237.43   8.523%   $257.6662   $257.67   $257.65   $257.70  
  7 purchase totals = $973.05       $1,059.7560   $1,059.76   $1,059.65   $1,059.80