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 $113.69   12.110%   $127.4579   $127.46   $127.45   $127.50  
  Purchase #2 $231.93   8.774%   $252.2795   $252.28   $252.30   $252.30  
  Purchase #3 $91.68   3.638%   $95.0153   $95.02   $95.00   $95.00  
  Purchase #4 $126.80   4.575%   $132.6011   $132.60   $132.60   $132.60  
  Purchase #5 $241.80   12.488%   $271.996   $272.00   $272.00   $272.00  
  Purchase #6 $213.47   4.154%   $222.3375   $222.34   $222.35   $222.30  
  Purchase #7 $228.72   11.337%   $254.65   $254.65   $254.65   $254.70  
  7 purchase totals = $1,248.09       $1,356.3373   $1,356.35   $1,356.35   $1,356.40