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 $60.31   10.654%   $66.7354   $66.74   $66.75   $66.70  
  Purchase #2 $155.77   13.814%   $177.2881   $177.29   $177.30   $177.30  
  Purchase #3 $42.49   13.644%   $48.2873   $48.29   $48.30   $48.30  
  Purchase #4 $233.35   12.744%   $263.0881   $263.09   $263.10   $263.10  
  Purchase #5 $239.27   4.159%   $249.2212   $249.22   $249.20   $249.20  
  Purchase #6 $212.73   6.243%   $226.0107   $226.01   $226.00   $226.00  
  Purchase #7 $31.70   8.668%   $34.4478   $34.45   $34.45   $34.40  
  7 purchase totals = $975.62       $1,065.0786   $1,065.09   $1,065.10   $1,065.00