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 $216.97   8.421%   $235.241   $235.24   $235.25   $235.20  
  Purchase #2 $110.78   5.500%   $116.8729   $116.87   $116.85   $116.90  
  Purchase #3 $78.65   11.116%   $87.3927   $87.39   $87.40   $87.40  
  Purchase #4 $198.61   3.236%   $205.037   $205.04   $205.05   $205.00  
  Purchase #5 $104.25   9.628%   $114.2872   $114.29   $114.30   $114.30  
  Purchase #6 $99.82   3.247%   $103.0612   $103.06   $103.05   $103.10  
  Purchase #7 $114.48   5.787%   $121.105   $121.11   $121.10   $121.10  
  7 purchase totals = $923.56       $982.9970   $983.00   $983.00   $983.00