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 $49.67   4.650%   $51.9797   $51.98   $52.00   $52.00  
  Purchase #2 $95.82   4.783%   $100.4031   $100.40   $100.40   $100.40  
  Purchase #3 $117.95   9.499%   $129.1541   $129.15   $129.15   $129.20  
  Purchase #4 $87.49   5.544%   $92.3404   $92.34   $92.35   $92.30  
  Purchase #5 $70.72   4.686%   $74.0339   $74.03   $74.05   $74.00  
  Purchase #6 $217.52   7.571%   $233.9884   $233.99   $234.00   $234.00  
  Purchase #7 $94.88   8.137%   $102.6004   $102.60   $102.60   $102.60  
  7 purchase totals = $734.05       $784.5000   $784.49   $784.55   $784.50