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 $168.44   9.819%   $184.9791   $184.98   $185.00   $185.00  
  Purchase #2 $39.77   12.775%   $44.8506   $44.85   $44.85   $44.90  
  Purchase #3 $33.69   12.110%   $37.7699   $37.77   $37.75   $37.80  
  Purchase #4 $204.37   11.767%   $228.4182   $228.42   $228.40   $228.40  
  Purchase #5 $244.26   7.614%   $262.858   $262.86   $262.85   $262.90  
  Purchase #6 $226.89   11.721%   $253.4838   $253.48   $253.50   $253.50  
  Purchase #7 $95.33   12.767%   $107.5008   $107.50   $107.50   $107.50  
  7 purchase totals = $1,012.75       $1,119.8604   $1,119.86   $1,119.85   $1,120.00