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 $68.82   7.181%   $73.762   $73.76   $73.75   $73.80  
  Purchase #2 $175.29   9.542%   $192.0162   $192.02   $192.00   $192.00  
  Purchase #3 $94.49   5.839%   $100.0073   $100.01   $100.00   $100.00  
  Purchase #4 $67.83   7.810%   $73.1275   $73.13   $73.15   $73.10  
  Purchase #5 $153.52   13.705%   $174.5599   $174.56   $174.55   $174.60  
  Purchase #6 $77.57   9.540%   $84.9702   $84.97   $84.95   $85.00  
  Purchase #7 $110.46   6.768%   $117.9359   $117.94   $117.95   $117.90  
  7 purchase totals = $747.98       $816.3790   $816.39   $816.35   $816.40