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 $157.37   12.216%   $176.5943   $176.59   $176.60   $176.60  
  Purchase #2 $99.65   12.141%   $111.7485   $111.75   $111.75   $111.70  
  Purchase #3 $65.36   6.625%   $69.6901   $69.69   $69.70   $69.70  
  Purchase #4 $206.90   5.293%   $217.8512   $217.85   $217.85   $217.90  
  Purchase #5 $139.55   11.287%   $155.301   $155.30   $155.30   $155.30  
  Purchase #6 $112.27   10.398%   $123.9438   $123.94   $123.95   $123.90  
  Purchase #7 $170.93   13.496%   $193.9987   $194.00   $194.00   $194.00  
  7 purchase totals = $952.03       $1,049.1276   $1,049.12   $1,049.15   $1,049.10