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 $184.43   7.760%   $198.7418   $198.74   $198.75   $198.70  
  Purchase #2 $24.77   10.353%   $27.3344   $27.33   $27.35   $27.30  
  Purchase #3 $104.99   13.868%   $119.55   $119.55   $119.55   $119.60  
  Purchase #4 $75.36   9.534%   $82.5448   $82.54   $82.55   $82.50  
  Purchase #5 $193.84   5.654%   $204.7997   $204.80   $204.80   $204.80  
  Purchase #6 $196.58   9.388%   $215.0349   $215.03   $215.05   $215.00  
  Purchase #7 $246.44   9.294%   $269.3441   $269.34   $269.35   $269.30  
  7 purchase totals = $1,026.41       $1,117.3497   $1,117.33   $1,117.40   $1,117.20