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 $228.97   5.576%   $241.7374   $241.74   $241.75   $241.70  
  Purchase #2 $218.46   3.405%   $225.8986   $225.90   $225.90   $225.90  
  Purchase #3 $93.49   11.270%   $104.0263   $104.03   $104.05   $104.00  
  Purchase #4 $148.40   10.444%   $163.8989   $163.90   $163.90   $163.90  
  Purchase #5 $50.90   7.722%   $54.8305   $54.83   $54.85   $54.80  
  Purchase #6 $49.30   10.221%   $54.339   $54.34   $54.35   $54.30  
  Purchase #7 $58.73   6.654%   $62.6379   $62.64   $62.65   $62.60  
  7 purchase totals = $848.25       $907.3686   $907.38   $907.45   $907.20