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 $58.89   10.165%   $64.8762   $64.88   $64.90   $64.90  
  Purchase #2 $147.75   11.569%   $164.8432   $164.84   $164.85   $164.80  
  Purchase #3 $25.65   6.210%   $27.2429   $27.24   $27.25   $27.20  
  Purchase #4 $210.92   3.723%   $218.7726   $218.77   $218.75   $218.80  
  Purchase #5 $22.43   5.760%   $23.722   $23.72   $23.70   $23.70  
  Purchase #6 $218.52   11.505%   $243.6607   $243.66   $243.65   $243.70  
  Purchase #7 $16.58   4.174%   $17.272   $17.27   $17.25   $17.30  
  7 purchase totals = $700.74       $760.3896   $760.38   $760.35   $760.40