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 $111.49   3.388%   $115.2673   $115.27   $115.25   $115.30  
  Purchase #2 $201.35   13.203%   $227.9342   $227.93   $227.95   $227.90  
  Purchase #3 $68.51   4.403%   $71.5265   $71.53   $71.55   $71.50  
  Purchase #4 $42.59   10.244%   $46.9529   $46.95   $46.95   $47.00  
  Purchase #5 $218.57   4.533%   $228.4778   $228.48   $228.50   $228.50  
  Purchase #6 $118.31   11.816%   $132.2895   $132.29   $132.30   $132.30  
  Purchase #7 $199.58   13.579%   $226.681   $226.68   $226.70   $226.70  
  7 purchase totals = $960.40       $1,049.1292   $1,049.13   $1,049.20   $1,049.20