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 $204.66   6.752%   $218.4786   $218.48   $218.50   $218.50  
  Purchase #2 $229.52   7.461%   $246.6445   $246.64   $246.65   $246.60  
  Purchase #3 $10.33   13.240%   $11.6977   $11.70   $11.70   $11.70  
  Purchase #4 $240.84   9.308%   $263.2574   $263.26   $263.25   $263.30  
  Purchase #5 $155.49   9.575%   $170.3782   $170.38   $170.40   $170.40  
  Purchase #6 $88.54   10.854%   $98.1501   $98.15   $98.15   $98.20  
  Purchase #7 $49.64   4.855%   $52.05   $52.05   $52.05   $52.10  
  7 purchase totals = $979.02       $1,060.6565   $1,060.66   $1,060.70   $1,060.80