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 $124.44   8.225%   $134.6752   $134.68   $134.70   $134.70  
  Purchase #2 $180.68   12.279%   $202.8657   $202.87   $202.85   $202.90  
  Purchase #3 $198.47   6.651%   $211.6702   $211.67   $211.65   $211.70  
  Purchase #4 $89.63   9.788%   $98.403   $98.40   $98.40   $98.40  
  Purchase #5 $224.96   5.728%   $237.8457   $237.85   $237.85   $237.80  
  Purchase #6 $53.42   13.368%   $60.5612   $60.56   $60.55   $60.60  
  Purchase #7 $69.65   6.851%   $74.4217   $74.42   $74.40   $74.40  
  7 purchase totals = $941.25       $1,020.4427   $1,020.45   $1,020.40   $1,020.50