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 $66.37   10.157%   $73.1112   $73.11   $73.10   $73.10  
  Purchase #2 $235.27   13.713%   $267.5326   $267.53   $267.55   $267.50  
  Purchase #3 $73.59   7.395%   $79.032   $79.03   $79.05   $79.00  
  Purchase #4 $41.89   9.165%   $45.7292   $45.73   $45.75   $45.70  
  Purchase #5 $115.65   10.239%   $127.4914   $127.49   $127.50   $127.50  
  Purchase #6 $208.94   6.762%   $223.0685   $223.07   $223.05   $223.10  
  Purchase #7 $38.97   8.651%   $42.3413   $42.34   $42.35   $42.30  
  7 purchase totals = $780.68       $858.3062   $858.30   $858.35   $858.20