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 $61.46   11.646%   $68.6176   $68.62   $68.60   $68.60  
  Purchase #2 $102.72   7.862%   $110.7958   $110.80   $110.80   $110.80  
  Purchase #3 $77.74   12.233%   $87.2499   $87.25   $87.25   $87.20  
  Purchase #4 $210.71   11.138%   $234.1789   $234.18   $234.20   $234.20  
  Purchase #5 $174.44   10.229%   $192.2835   $192.28   $192.30   $192.30  
  Purchase #6 $219.31   12.582%   $246.9036   $246.90   $246.90   $246.90  
  Purchase #7 $172.93   8.550%   $187.7155   $187.72   $187.70   $187.70  
  7 purchase totals = $1,019.31       $1,127.7448   $1,127.75   $1,127.75   $1,127.70