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 $247.59   10.463%   $273.4953   $273.50   $273.50   $273.50  
  Purchase #2 $206.64   10.850%   $229.0604   $229.06   $229.05   $229.10  
  Purchase #3 $148.32   11.722%   $165.7061   $165.71   $165.70   $165.70  
  Purchase #4 $55.68   9.633%   $61.0437   $61.04   $61.05   $61.00  
  Purchase #5 $222.92   13.655%   $253.3597   $253.36   $253.35   $253.40  
  Purchase #6 $211.29   7.587%   $227.3206   $227.32   $227.30   $227.30  
  Purchase #7 $227.64   3.479%   $235.5596   $235.56   $235.55   $235.60  
  7 purchase totals = $1,320.08       $1,445.5454   $1,445.55   $1,445.50   $1,445.60