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 $198.35   5.858%   $209.9693   $209.97   $209.95   $210.00  
  Purchase #2 $244.94   6.334%   $260.4545   $260.45   $260.45   $260.50  
  Purchase #3 $77.65   5.744%   $82.1102   $82.11   $82.10   $82.10  
  Purchase #4 $41.25   7.272%   $44.2497   $44.25   $44.25   $44.20  
  Purchase #5 $120.84   8.853%   $131.538   $131.54   $131.55   $131.50  
  Purchase #6 $116.60   5.652%   $123.1902   $123.19   $123.20   $123.20  
  Purchase #7 $100.37   12.760%   $113.1772   $113.18   $113.20   $113.20  
  7 purchase totals = $900.00       $964.6891   $964.69   $964.70   $964.70