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 $65.69   11.868%   $73.4861   $73.49   $73.50   $73.50  
  Purchase #2 $147.66   12.428%   $166.0112   $166.01   $166.00   $166.00  
  Purchase #3 $234.44   10.729%   $259.5931   $259.59   $259.60   $259.60  
  Purchase #4 $36.25   5.778%   $38.3445   $38.34   $38.35   $38.30  
  Purchase #5 $163.35   7.322%   $175.3105   $175.31   $175.30   $175.30  
  Purchase #6 $96.61   7.378%   $103.7379   $103.74   $103.75   $103.70  
  Purchase #7 $204.62   13.442%   $232.125   $232.13   $232.15   $232.10  
  7 purchase totals = $948.62       $1,048.6083   $1,048.61   $1,048.65   $1,048.50