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 $56.94   12.123%   $63.8428   $63.84   $63.85   $63.80  
  Purchase #2 $59.86   10.153%   $65.9376   $65.94   $65.95   $65.90  
  Purchase #3 $207.89   7.125%   $222.7022   $222.70   $222.70   $222.70  
  Purchase #4 $219.99   4.791%   $230.5297   $230.53   $230.55   $230.50  
  Purchase #5 $83.29   5.260%   $87.6711   $87.67   $87.65   $87.70  
  Purchase #6 $222.91   13.609%   $253.2458   $253.25   $253.25   $253.20  
  Purchase #7 $119.71   13.132%   $135.4303   $135.43   $135.45   $135.40  
  7 purchase totals = $970.59       $1,059.3595   $1,059.36   $1,059.40   $1,059.20