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 $68.82   5.457%   $72.5755   $72.58   $72.60   $72.60  
  Purchase #2 $184.44   5.671%   $194.8996   $194.90   $194.90   $194.90  
  Purchase #3 $128.32   4.421%   $133.993   $133.99   $134.00   $134.00  
  Purchase #4 $214.51   6.131%   $227.6616   $227.66   $227.65   $227.70  
  Purchase #5 $122.48   7.190%   $131.2863   $131.29   $131.30   $131.30  
  Purchase #6 $15.34   9.474%   $16.7933   $16.79   $16.80   $16.80  
  Purchase #7 $86.82   11.381%   $96.701   $96.70   $96.70   $96.70  
  7 purchase totals = $820.73       $873.9103   $873.91   $873.95   $874.00