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 $203.61   10.806%   $225.6121   $225.61   $225.60   $225.60  
  Purchase #2 $190.48   10.773%   $211.0004   $211.00   $211.00   $211.00  
  Purchase #3 $10.89   12.252%   $12.2242   $12.22   $12.20   $12.20  
  Purchase #4 $126.73   4.440%   $132.3568   $132.36   $132.35   $132.40  
  Purchase #5 $202.90   6.399%   $215.8836   $215.88   $215.90   $215.90  
  Purchase #6 $110.61   5.849%   $117.0796   $117.08   $117.10   $117.10  
  Purchase #7 $224.86   3.831%   $233.4744   $233.47   $233.45   $233.50  
  7 purchase totals = $1,070.08       $1,147.6311   $1,147.62   $1,147.60   $1,147.70