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 $56.92   3.635%   $58.989   $58.99   $59.00   $59.00  
  Purchase #2 $140.47   8.707%   $152.7007   $152.70   $152.70   $152.70  
  Purchase #3 $81.91   12.284%   $91.9718   $91.97   $91.95   $92.00  
  Purchase #4 $99.86   6.483%   $106.3339   $106.33   $106.35   $106.30  
  Purchase #5 $152.72   13.597%   $173.4853   $173.49   $173.50   $173.50  
  Purchase #6 $103.36   9.758%   $113.4459   $113.45   $113.45   $113.40  
  Purchase #7 $91.39   3.118%   $94.2395   $94.24   $94.25   $94.20  
  7 purchase totals = $726.63       $791.1661   $791.17   $791.20   $791.10