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 $242.52   3.502%   $251.0131   $251.01   $251.00   $251.00  
  Purchase #2 $230.47   3.601%   $238.7692   $238.77   $238.75   $238.80  
  Purchase #3 $235.64   11.477%   $262.6844   $262.68   $262.70   $262.70  
  Purchase #4 $81.36   11.556%   $90.762   $90.76   $90.75   $90.80  
  Purchase #5 $87.37   4.869%   $91.624   $91.62   $91.60   $91.60  
  Purchase #6 $11.26   5.852%   $11.9189   $11.92   $11.90   $11.90  
  Purchase #7 $61.80   3.278%   $63.8258   $63.83   $63.85   $63.80  
  7 purchase totals = $950.42       $1,010.5974   $1,010.59   $1,010.55   $1,010.60