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 $76.55   11.182%   $85.1098   $85.11   $85.10   $85.10  
  Purchase #2 $78.91   11.147%   $87.7061   $87.71   $87.70   $87.70  
  Purchase #3 $147.89   12.559%   $166.4635   $166.46   $166.45   $166.50  
  Purchase #4 $234.37   13.650%   $266.3615   $266.36   $266.35   $266.40  
  Purchase #5 $215.45   4.867%   $225.936   $225.94   $225.95   $225.90  
  Purchase #6 $193.75   5.184%   $203.794   $203.79   $203.80   $203.80  
  Purchase #7 $228.86   7.530%   $246.0932   $246.09   $246.10   $246.10  
  7 purchase totals = $1,175.78       $1,281.4641   $1,281.46   $1,281.45   $1,281.50