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 $163.91   12.667%   $184.6725   $184.67   $184.65   $184.70  
  Purchase #2 $232.99   4.528%   $243.5398   $243.54   $243.55   $243.50  
  Purchase #3 $235.43   6.825%   $251.4981   $251.50   $251.50   $251.50  
  Purchase #4 $250.35   9.395%   $273.8704   $273.87   $273.85   $273.90  
  Purchase #5 $164.85   4.307%   $171.9501   $171.95   $171.95   $172.00  
  Purchase #6 $12.95   10.757%   $14.343   $14.34   $14.35   $14.30  
  Purchase #7 $201.55   13.387%   $228.5315   $228.53   $228.55   $228.50  
  7 purchase totals = $1,262.03       $1,368.4054   $1,368.40   $1,368.40   $1,368.40