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 $218.52   13.841%   $248.7654   $248.77   $248.75   $248.80  
  Purchase #2 $75.97   12.772%   $85.6729   $85.67   $85.65   $85.70  
  Purchase #3 $143.86   10.524%   $158.9998   $159.00   $159.00   $159.00  
  Purchase #4 $16.77   13.621%   $19.0542   $19.05   $19.05   $19.10  
  Purchase #5 $177.31   8.107%   $191.6845   $191.68   $191.70   $191.70  
  Purchase #6 $231.28   13.780%   $263.1504   $263.15   $263.15   $263.20  
  Purchase #7 $154.42   6.147%   $163.9122   $163.91   $163.90   $163.90  
  7 purchase totals = $1,018.13       $1,131.2394   $1,131.23   $1,131.20   $1,131.40