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 $9.33   4.223%   $9.724   $9.72   $9.70   $9.70  
  Purchase #2 $153.92   8.171%   $166.4968   $166.50   $166.50   $166.50  
  Purchase #3 $138.45   8.332%   $149.9857   $149.99   $150.00   $150.00  
  Purchase #4 $225.98   9.750%   $248.0131   $248.01   $248.00   $248.00  
  Purchase #5 $192.60   5.226%   $202.6653   $202.67   $202.65   $202.70  
  Purchase #6 $180.62   6.353%   $192.0948   $192.09   $192.10   $192.10  
  Purchase #7 $5.47   6.308%   $5.815   $5.82   $5.80   $5.80  
  7 purchase totals = $906.37       $974.7947   $974.80   $974.75   $974.80