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 $84.36   10.828%   $93.4945   $93.49   $93.50   $93.50  
  Purchase #2 $107.47   10.343%   $118.5856   $118.59   $118.60   $118.60  
  Purchase #3 $162.67   6.147%   $172.6693   $172.67   $172.65   $172.70  
  Purchase #4 $113.30   11.701%   $126.5572   $126.56   $126.55   $126.60  
  Purchase #5 $222.60   11.619%   $248.4639   $248.46   $248.45   $248.50  
  Purchase #6 $170.89   6.124%   $181.3553   $181.36   $181.35   $181.40  
  Purchase #7 $58.30   9.485%   $63.8298   $63.83   $63.85   $63.80  
  7 purchase totals = $919.59       $1,004.9556   $1,004.96   $1,004.95   $1,005.10