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 $77.45   13.616%   $87.9956   $88.00   $88.00   $88.00  
  Purchase #2 $241.60   10.369%   $266.6515   $266.65   $266.65   $266.70  
  Purchase #3 $80.48   6.376%   $85.6114   $85.61   $85.60   $85.60  
  Purchase #4 $170.69   13.534%   $193.7912   $193.79   $193.80   $193.80  
  Purchase #5 $35.89   10.635%   $39.7069   $39.71   $39.70   $39.70  
  Purchase #6 $54.55   3.824%   $56.636   $56.64   $56.65   $56.60  
  Purchase #7 $22.30   12.178%   $25.0157   $25.02   $25.00   $25.00  
  7 purchase totals = $682.96       $755.4083   $755.42   $755.40   $755.40