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 $226.47   13.489%   $257.0185   $257.02   $257.00   $257.00  
  Purchase #2 $79.25   8.579%   $86.0489   $86.05   $86.05   $86.00  
  Purchase #3 $185.34   6.224%   $196.8756   $196.88   $196.90   $196.90  
  Purchase #4 $62.52   11.692%   $69.8298   $69.83   $69.85   $69.80  
  Purchase #5 $165.79   8.170%   $179.335   $179.34   $179.35   $179.30  
  Purchase #6 $89.25   12.800%   $100.674   $100.67   $100.65   $100.70  
  Purchase #7 $212.39   10.381%   $234.4382   $234.44   $234.45   $234.40  
  7 purchase totals = $1,021.01       $1,124.2200   $1,124.23   $1,124.25   $1,124.10