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 $65.78   3.321%   $67.9646   $67.96   $67.95   $68.00  
  Purchase #2 $124.89   7.276%   $133.977   $133.98   $134.00   $134.00  
  Purchase #3 $240.65   13.698%   $273.6142   $273.61   $273.60   $273.60  
  Purchase #4 $241.56   12.120%   $270.8371   $270.84   $270.85   $270.80  
  Purchase #5 $62.74   3.173%   $64.7307   $64.73   $64.75   $64.70  
  Purchase #6 $115.75   8.631%   $125.7404   $125.74   $125.75   $125.70  
  Purchase #7 $140.30   8.340%   $152.001   $152.00   $152.00   $152.00  
  7 purchase totals = $991.67       $1,088.8650   $1,088.86   $1,088.90   $1,088.80