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 $61.47   5.711%   $64.9806   $64.98   $65.00   $65.00  
  Purchase #2 $154.70   6.156%   $164.2233   $164.22   $164.20   $164.20  
  Purchase #3 $65.89   7.653%   $70.9326   $70.93   $70.95   $70.90  
  Purchase #4 $163.29   5.698%   $172.5943   $172.59   $172.60   $172.60  
  Purchase #5 $7.60   9.394%   $8.3139   $8.31   $8.30   $8.30  
  Purchase #6 $206.58   9.750%   $226.7216   $226.72   $226.70   $226.70  
  Purchase #7 $194.55   8.307%   $210.7113   $210.71   $210.70   $210.70  
  7 purchase totals = $854.08       $918.4776   $918.46   $918.45   $918.40