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 $140.96   9.499%   $154.3498   $154.35   $154.35   $154.30  
  Purchase #2 $167.77   4.342%   $175.0546   $175.05   $175.05   $175.10  
  Purchase #3 $101.55   8.463%   $110.1442   $110.14   $110.15   $110.10  
  Purchase #4 $152.51   6.830%   $162.9264   $162.93   $162.95   $162.90  
  Purchase #5 $63.69   8.322%   $68.9903   $68.99   $69.00   $69.00  
  Purchase #6 $222.91   4.749%   $233.496   $233.50   $233.50   $233.50  
  Purchase #7 $163.47   10.110%   $179.9968   $180.00   $180.00   $180.00  
  7 purchase totals = $1,012.86       $1,084.9581   $1,084.96   $1,085.00   $1,084.90