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 $246.62   11.516%   $275.0208   $275.02   $275.00   $275.00  
  Purchase #2 $137.35   10.787%   $152.1659   $152.17   $152.15   $152.20  
  Purchase #3 $24.41   7.451%   $26.2288   $26.23   $26.25   $26.20  
  Purchase #4 $214.91   10.413%   $237.2886   $237.29   $237.30   $237.30  
  Purchase #5 $62.87   7.394%   $67.5186   $67.52   $67.50   $67.50  
  Purchase #6 $76.25   8.629%   $82.8296   $82.83   $82.85   $82.80  
  Purchase #7 $185.92   13.472%   $210.9671   $210.97   $210.95   $211.00  
  7 purchase totals = $948.33       $1,052.0194   $1,052.03   $1,052.00   $1,052.00