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 $219.65   12.864%   $247.9058   $247.91   $247.90   $247.90  
  Purchase #2 $206.48   11.368%   $229.9526   $229.95   $229.95   $230.00  
  Purchase #3 $22.81   12.724%   $25.7123   $25.71   $25.70   $25.70  
  Purchase #4 $49.92   10.855%   $55.3388   $55.34   $55.35   $55.30  
  Purchase #5 $152.81   4.647%   $159.9111   $159.91   $159.90   $159.90  
  Purchase #6 $97.57   7.131%   $104.5277   $104.53   $104.55   $104.50  
  Purchase #7 $243.30   13.259%   $275.5591   $275.56   $275.55   $275.60  
  7 purchase totals = $992.54       $1,098.9074   $1,098.91   $1,098.90   $1,098.90