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 $233.59   8.123%   $252.5645   $252.56   $252.55   $252.60  
  Purchase #2 $62.90   7.668%   $67.7232   $67.72   $67.70   $67.70  
  Purchase #3 $57.90   9.590%   $63.4526   $63.45   $63.45   $63.50  
  Purchase #4 $171.44   12.683%   $193.1837   $193.18   $193.20   $193.20  
  Purchase #5 $132.39   13.742%   $150.583   $150.58   $150.60   $150.60  
  Purchase #6 $56.78   11.425%   $63.2671   $63.27   $63.25   $63.30  
  Purchase #7 $232.49   7.849%   $250.7381   $250.74   $250.75   $250.70  
  7 purchase totals = $947.49       $1,041.5122   $1,041.50   $1,041.50   $1,041.60