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 $113.67   3.817%   $118.0088   $118.01   $118.00   $118.00  
  Purchase #2 $106.97   6.417%   $113.8343   $113.83   $113.85   $113.80  
  Purchase #3 $196.75   6.596%   $209.7276   $209.73   $209.75   $209.70  
  Purchase #4 $107.99   9.394%   $118.1346   $118.13   $118.15   $118.10  
  Purchase #5 $198.54   4.166%   $206.8112   $206.81   $206.80   $206.80  
  Purchase #6 $167.30   10.401%   $184.7009   $184.70   $184.70   $184.70  
  Purchase #7 $234.88   6.446%   $250.0204   $250.02   $250.00   $250.00  
  7 purchase totals = $1,126.10       $1,201.2378   $1,201.23   $1,201.25   $1,201.10