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 $92.88   3.381%   $96.0203   $96.02   $96.00   $96.00  
  Purchase #2 $85.87   11.665%   $95.8867   $95.89   $95.90   $95.90  
  Purchase #3 $52.65   6.333%   $55.9843   $55.98   $56.00   $56.00  
  Purchase #4 $41.39   8.641%   $44.9665   $44.97   $44.95   $45.00  
  Purchase #5 $13.95   5.834%   $14.7638   $14.76   $14.75   $14.80  
  Purchase #6 $171.63   13.335%   $194.5169   $194.52   $194.50   $194.50  
  Purchase #7 $87.49   6.843%   $93.4769   $93.48   $93.50   $93.50  
  7 purchase totals = $545.86       $595.6154   $595.62   $595.60   $595.70