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 $59.50   7.631%   $64.0404   $64.04   $64.05   $64.00  
  Purchase #2 $23.40   11.286%   $26.0409   $26.04   $26.05   $26.00  
  Purchase #3 $198.45   13.201%   $224.6474   $224.65   $224.65   $224.60  
  Purchase #4 $155.74   3.283%   $160.8529   $160.85   $160.85   $160.90  
  Purchase #5 $79.46   10.701%   $87.963   $87.96   $87.95   $88.00  
  Purchase #6 $19.69   4.284%   $20.5335   $20.53   $20.55   $20.50  
  Purchase #7 $214.95   11.188%   $238.9986   $239.00   $239.00   $239.00  
  7 purchase totals = $751.19       $823.0767   $823.07   $823.10   $823.00