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 $76.96   11.771%   $86.019   $86.02   $86.00   $86.00  
  Purchase #2 $58.34   4.190%   $60.7844   $60.78   $60.80   $60.80  
  Purchase #3 $77.70   6.869%   $83.0372   $83.04   $83.05   $83.00  
  Purchase #4 $138.55   6.253%   $147.2135   $147.21   $147.20   $147.20  
  Purchase #5 $66.68   10.455%   $73.6514   $73.65   $73.65   $73.70  
  Purchase #6 $222.44   12.569%   $250.3985   $250.40   $250.40   $250.40  
  Purchase #7 $111.52   9.454%   $122.0631   $122.06   $122.05   $122.10  
  7 purchase totals = $752.19       $823.1671   $823.16   $823.15   $823.20