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 $70.81   9.145%   $77.2856   $77.29   $77.30   $77.30  
  Purchase #2 $200.48   12.708%   $225.957   $225.96   $225.95   $226.00  
  Purchase #3 $9.81   10.677%   $10.8574   $10.86   $10.85   $10.90  
  Purchase #4 $192.96   9.626%   $211.5343   $211.53   $211.55   $211.50  
  Purchase #5 $202.43   8.507%   $219.6507   $219.65   $219.65   $219.70  
  Purchase #6 $179.96   4.737%   $188.4847   $188.48   $188.50   $188.50  
  Purchase #7 $60.37   3.507%   $62.4872   $62.49   $62.50   $62.50  
  7 purchase totals = $916.82       $996.2569   $996.26   $996.30   $996.40