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 $82.59   13.237%   $93.5224   $93.52   $93.50   $93.50  
  Purchase #2 $161.83   6.277%   $171.9881   $171.99   $172.00   $172.00  
  Purchase #3 $71.33   6.183%   $75.7403   $75.74   $75.75   $75.70  
  Purchase #4 $157.83   12.116%   $176.9527   $176.95   $176.95   $177.00  
  Purchase #5 $143.51   4.106%   $149.4025   $149.40   $149.40   $149.40  
  Purchase #6 $239.60   4.339%   $249.9962   $250.00   $250.00   $250.00  
  Purchase #7 $220.83   9.582%   $241.9899   $241.99   $242.00   $242.00  
  7 purchase totals = $1,077.52       $1,159.5921   $1,159.59   $1,159.60   $1,159.60