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 $86.97   4.779%   $91.1263   $91.13   $91.15   $91.10  
  Purchase #2 $113.46   13.411%   $128.6761   $128.68   $128.70   $128.70  
  Purchase #3 $195.86   8.122%   $211.7677   $211.77   $211.75   $211.80  
  Purchase #4 $32.81   3.332%   $33.9032   $33.90   $33.90   $33.90  
  Purchase #5 $132.32   10.713%   $146.4954   $146.50   $146.50   $146.50  
  Purchase #6 $192.52   13.363%   $218.2464   $218.25   $218.25   $218.20  
  Purchase #7 $227.41   8.623%   $247.0196   $247.02   $247.00   $247.00  
  7 purchase totals = $981.35       $1,077.2347   $1,077.25   $1,077.25   $1,077.20