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 $155.35   12.661%   $175.0189   $175.02   $175.00   $175.00  
  Purchase #2 $96.99   7.704%   $104.4621   $104.46   $104.45   $104.50  
  Purchase #3 $170.62   6.537%   $181.7734   $181.77   $181.75   $181.80  
  Purchase #4 $212.82   12.532%   $239.4906   $239.49   $239.50   $239.50  
  Purchase #5 $27.67   12.283%   $31.0687   $31.07   $31.05   $31.10  
  Purchase #6 $178.65   3.789%   $185.419   $185.42   $185.40   $185.40  
  Purchase #7 $233.74   13.589%   $265.5029   $265.50   $265.50   $265.50  
  7 purchase totals = $1,075.84       $1,182.7356   $1,182.73   $1,182.65   $1,182.80