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 $26.35   11.783%   $29.4548   $29.45   $29.45   $29.50  
  Purchase #2 $34.42   5.731%   $36.3926   $36.39   $36.40   $36.40  
  Purchase #3 $213.51   4.715%   $223.577   $223.58   $223.60   $223.60  
  Purchase #4 $68.30   4.235%   $71.1925   $71.19   $71.20   $71.20  
  Purchase #5 $235.74   3.429%   $243.8235   $243.82   $243.80   $243.80  
  Purchase #6 $14.33   7.168%   $15.3572   $15.36   $15.35   $15.40  
  Purchase #7 $216.34   13.318%   $245.1522   $245.15   $245.15   $245.20  
  7 purchase totals = $808.99       $864.9498   $864.94   $864.95   $865.10