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 $113.99   10.588%   $126.0593   $126.06   $126.05   $126.10  
  Purchase #2 $129.62   3.668%   $134.3745   $134.37   $134.35   $134.40  
  Purchase #3 $162.27   7.422%   $174.3137   $174.31   $174.30   $174.30  
  Purchase #4 $240.98   4.873%   $252.723   $252.72   $252.70   $252.70  
  Purchase #5 $7.46   4.603%   $7.8034   $7.80   $7.80   $7.80  
  Purchase #6 $211.81   11.120%   $235.3633   $235.36   $235.35   $235.40  
  Purchase #7 $75.71   3.658%   $78.4795   $78.48   $78.50   $78.50  
  7 purchase totals = $941.84       $1,009.1167   $1,009.10   $1,009.05   $1,009.20