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 $91.51   3.704%   $94.8995   $94.90   $94.90   $94.90  
  Purchase #2 $157.77   11.544%   $175.983   $175.98   $176.00   $176.00  
  Purchase #3 $141.29   4.223%   $147.2567   $147.26   $147.25   $147.30  
  Purchase #4 $140.58   8.331%   $152.2917   $152.29   $152.30   $152.30  
  Purchase #5 $56.27   11.454%   $62.7152   $62.72   $62.70   $62.70  
  Purchase #6 $43.73   6.794%   $46.701   $46.70   $46.70   $46.70  
  Purchase #7 $108.97   13.278%   $123.439   $123.44   $123.45   $123.40  
  7 purchase totals = $740.12       $803.2861   $803.29   $803.30   $803.30