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 $124.64   11.141%   $138.5261   $138.53   $138.55   $138.50  
  Purchase #2 $41.62   4.256%   $43.3913   $43.39   $43.40   $43.40  
  Purchase #3 $82.49   6.349%   $87.7273   $87.73   $87.75   $87.70  
  Purchase #4 $219.48   10.144%   $241.7441   $241.74   $241.75   $241.70  
  Purchase #5 $93.56   3.276%   $96.625   $96.63   $96.65   $96.60  
  Purchase #6 $64.64   3.691%   $67.0259   $67.03   $67.05   $67.00  
  Purchase #7 $74.60   7.693%   $80.339   $80.34   $80.35   $80.30  
  7 purchase totals = $701.03       $755.3787   $755.39   $755.50   $755.20