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 $250.83   13.604%   $284.9529   $284.95   $284.95   $285.00  
  Purchase #2 $211.93   7.820%   $228.5029   $228.50   $228.50   $228.50  
  Purchase #3 $199.29   10.736%   $220.6858   $220.69   $220.70   $220.70  
  Purchase #4 $45.78   7.796%   $49.349   $49.35   $49.35   $49.30  
  Purchase #5 $112.41   10.589%   $124.3131   $124.31   $124.30   $124.30  
  Purchase #6 $113.69   12.345%   $127.725   $127.73   $127.75   $127.70  
  Purchase #7 $154.60   3.581%   $160.1362   $160.14   $160.15   $160.10  
  7 purchase totals = $1,088.53       $1,195.6649   $1,195.67   $1,195.70   $1,195.60