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 $167.84   11.761%   $187.5797   $187.58   $187.60   $187.60  
  Purchase #2 $163.80   13.480%   $185.8802   $185.88   $185.90   $185.90  
  Purchase #3 $228.69   6.242%   $242.9648   $242.96   $242.95   $243.00  
  Purchase #4 $218.89   10.239%   $241.3021   $241.30   $241.30   $241.30  
  Purchase #5 $50.75   4.611%   $53.0901   $53.09   $53.10   $53.10  
  Purchase #6 $212.68   5.536%   $224.454   $224.45   $224.45   $224.50  
  Purchase #7 $230.62   4.677%   $241.4061   $241.41   $241.40   $241.40  
  7 purchase totals = $1,273.27       $1,376.6770   $1,376.67   $1,376.70   $1,376.80