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 $70.63   6.173%   $74.99   $74.99   $75.00   $75.00  
  Purchase #2 $165.27   4.282%   $172.3469   $172.35   $172.35   $172.30  
  Purchase #3 $103.98   12.255%   $116.7227   $116.72   $116.70   $116.70  
  Purchase #4 $41.30   7.720%   $44.4884   $44.49   $44.50   $44.50  
  Purchase #5 $240.78   11.124%   $267.5644   $267.56   $267.55   $267.60  
  Purchase #6 $168.36   11.751%   $188.144   $188.14   $188.15   $188.10  
  Purchase #7 $112.55   8.673%   $122.3115   $122.31   $122.30   $122.30  
  7 purchase totals = $902.87       $986.5679   $986.56   $986.55   $986.50