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 $228.86   7.759%   $246.6172   $246.62   $246.60   $246.60  
  Purchase #2 $110.44   5.771%   $116.8135   $116.81   $116.80   $116.80  
  Purchase #3 $47.65   12.667%   $53.6858   $53.69   $53.70   $53.70  
  Purchase #4 $192.33   5.812%   $203.5082   $203.51   $203.50   $203.50  
  Purchase #5 $227.48   5.223%   $239.3613   $239.36   $239.35   $239.40  
  Purchase #6 $166.94   13.699%   $189.8091   $189.81   $189.80   $189.80  
  Purchase #7 $173.49   10.577%   $191.84   $191.84   $191.85   $191.80  
  7 purchase totals = $1,147.19       $1,241.6351   $1,241.64   $1,241.60   $1,241.60