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 $59.59   3.804%   $61.8568   $61.86   $61.85   $61.90  
  Purchase #2 $28.57   4.325%   $29.8057   $29.81   $29.80   $29.80  
  Purchase #3 $248.32   3.619%   $257.3067   $257.31   $257.30   $257.30  
  Purchase #4 $231.55   6.827%   $247.3579   $247.36   $247.35   $247.40  
  Purchase #5 $236.37   3.591%   $244.858   $244.86   $244.85   $244.90  
  Purchase #6 $169.69   6.487%   $180.6978   $180.70   $180.70   $180.70  
  Purchase #7 $16.46   11.450%   $18.3447   $18.34   $18.35   $18.30  
  7 purchase totals = $990.55       $1,040.2276   $1,040.24   $1,040.20   $1,040.30