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 $82.78   11.449%   $92.2575   $92.26   $92.25   $92.30  
  Purchase #2 $110.85   8.513%   $120.2867   $120.29   $120.30   $120.30  
  Purchase #3 $171.39   8.552%   $186.0473   $186.05   $186.05   $186.00  
  Purchase #4 $221.91   9.531%   $243.0602   $243.06   $243.05   $243.10  
  Purchase #5 $212.61   9.148%   $232.0596   $232.06   $232.05   $232.10  
  Purchase #6 $157.60   11.363%   $175.5081   $175.51   $175.50   $175.50  
  Purchase #7 $162.44   13.698%   $184.691   $184.69   $184.70   $184.70  
  7 purchase totals = $1,119.58       $1,233.9104   $1,233.92   $1,233.90   $1,234.00