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 $152.98   4.133%   $159.3027   $159.30   $159.30   $159.30  
  Purchase #2 $90.55   13.529%   $102.8005   $102.80   $102.80   $102.80  
  Purchase #3 $26.28   9.783%   $28.851   $28.85   $28.85   $28.90  
  Purchase #4 $196.45   7.206%   $210.6062   $210.61   $210.60   $210.60  
  Purchase #5 $149.96   10.458%   $165.6428   $165.64   $165.65   $165.60  
  Purchase #6 $70.94   5.311%   $74.7076   $74.71   $74.70   $74.70  
  Purchase #7 $107.68   13.351%   $122.0564   $122.06   $122.05   $122.10  
  7 purchase totals = $794.84       $863.9672   $863.97   $863.95   $864.00