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 $58.78   6.248%   $62.4526   $62.45   $62.45   $62.50  
  Purchase #2 $157.62   11.280%   $175.3995   $175.40   $175.40   $175.40  
  Purchase #3 $202.81   12.610%   $228.3843   $228.38   $228.40   $228.40  
  Purchase #4 $121.59   13.201%   $137.6411   $137.64   $137.65   $137.60  
  Purchase #5 $211.81   6.818%   $226.2512   $226.25   $226.25   $226.30  
  Purchase #6 $96.75   7.770%   $104.2675   $104.27   $104.25   $104.30  
  Purchase #7 $236.49   13.799%   $269.1233   $269.12   $269.10   $269.10  
  7 purchase totals = $1,085.85       $1,203.5195   $1,203.51   $1,203.50   $1,203.60