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 $58.44   4.338%   $60.9751   $60.98   $61.00   $61.00  
  Purchase #2 $95.62   12.143%   $107.2311   $107.23   $107.25   $107.20  
  Purchase #3 $62.30   10.436%   $68.8016   $68.80   $68.80   $68.80  
  Purchase #4 $143.76   3.511%   $148.8074   $148.81   $148.80   $148.80  
  Purchase #5 $174.25   4.747%   $182.5216   $182.52   $182.50   $182.50  
  Purchase #6 $149.89   7.159%   $160.6206   $160.62   $160.60   $160.60  
  Purchase #7 $233.35   8.408%   $252.9701   $252.97   $252.95   $253.00  
  7 purchase totals = $917.61       $981.9275   $981.93   $981.90   $981.90