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 $222.86   11.353%   $248.1613   $248.16   $248.15   $248.20  
  Purchase #2 $41.62   4.844%   $43.6361   $43.64   $43.65   $43.60  
  Purchase #3 $120.72   6.474%   $128.5354   $128.54   $128.55   $128.50  
  Purchase #4 $80.37   9.856%   $88.2913   $88.29   $88.30   $88.30  
  Purchase #5 $233.55   5.714%   $246.895   $246.90   $246.90   $246.90  
  Purchase #6 $177.26   10.228%   $195.3902   $195.39   $195.40   $195.40  
  Purchase #7 $223.49   5.266%   $235.259   $235.26   $235.25   $235.30  
  7 purchase totals = $1,099.87       $1,186.1683   $1,186.18   $1,186.20   $1,186.20