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 $30.78   11.254%   $34.244   $34.24   $34.25   $34.20  
  Purchase #2 $59.44   5.114%   $62.4798   $62.48   $62.50   $62.50  
  Purchase #3 $226.92   9.424%   $248.3049   $248.30   $248.30   $248.30  
  Purchase #4 $160.74   7.474%   $172.7537   $172.75   $172.75   $172.80  
  Purchase #5 $183.33   13.404%   $207.9036   $207.90   $207.90   $207.90  
  Purchase #6 $69.60   8.689%   $75.6475   $75.65   $75.65   $75.60  
  Purchase #7 $193.86   3.534%   $200.711   $200.71   $200.70   $200.70  
  7 purchase totals = $924.67       $1,002.0445   $1,002.03   $1,002.05   $1,002.00