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 $93.92   11.369%   $104.5978   $104.60   $104.60   $104.60  
  Purchase #2 $175.35   9.600%   $192.1836   $192.18   $192.20   $192.20  
  Purchase #3 $56.71   8.670%   $61.6268   $61.63   $61.65   $61.60  
  Purchase #4 $80.38   13.809%   $91.4797   $91.48   $91.50   $91.50  
  Purchase #5 $225.78   12.330%   $253.6187   $253.62   $253.60   $253.60  
  Purchase #6 $202.29   7.264%   $216.9843   $216.98   $217.00   $217.00  
  Purchase #7 $132.49   9.258%   $144.7559   $144.76   $144.75   $144.80  
  7 purchase totals = $966.92       $1,065.2468   $1,065.25   $1,065.30   $1,065.30