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 $29.42   9.603%   $32.2452   $32.25   $32.25   $32.20  
  Purchase #2 $190.86   4.688%   $199.8075   $199.81   $199.80   $199.80  
  Purchase #3 $65.99   12.247%   $74.0718   $74.07   $74.05   $74.10  
  Purchase #4 $50.78   4.235%   $52.9305   $52.93   $52.95   $52.90  
  Purchase #5 $196.34   12.391%   $220.6685   $220.67   $220.65   $220.70  
  Purchase #6 $80.64   6.577%   $85.9437   $85.94   $85.95   $85.90  
  Purchase #7 $39.95   4.104%   $41.5895   $41.59   $41.60   $41.60  
  7 purchase totals = $653.98       $707.2567   $707.26   $707.25   $707.20