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 $189.71   11.812%   $212.1185   $212.12   $212.10   $212.10  
  Purchase #2 $234.41   5.768%   $247.9308   $247.93   $247.95   $247.90  
  Purchase #3 $228.91   4.144%   $238.396   $238.40   $238.40   $238.40  
  Purchase #4 $150.39   8.653%   $163.4032   $163.40   $163.40   $163.40  
  Purchase #5 $156.32   13.815%   $177.9156   $177.92   $177.90   $177.90  
  Purchase #6 $195.27   11.814%   $218.3392   $218.34   $218.35   $218.30  
  Purchase #7 $9.40   3.391%   $9.7188   $9.72   $9.70   $9.70  
  7 purchase totals = $1,164.41       $1,267.8221   $1,267.83   $1,267.80   $1,267.70