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 $61.54   8.159%   $66.561   $66.56   $66.55   $66.60  
  Purchase #2 $249.98   7.639%   $269.076   $269.08   $269.10   $269.10  
  Purchase #3 $113.54   3.647%   $117.6808   $117.68   $117.70   $117.70  
  Purchase #4 $54.82   3.849%   $56.93   $56.93   $56.95   $56.90  
  Purchase #5 $19.82   11.836%   $22.1659   $22.17   $22.15   $22.20  
  Purchase #6 $214.33   13.475%   $243.211   $243.21   $243.20   $243.20  
  Purchase #7 $107.58   12.353%   $120.8694   $120.87   $120.85   $120.90  
  7 purchase totals = $821.61       $896.4941   $896.50   $896.50   $896.60