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 $124.80   13.654%   $141.8402   $141.84   $141.85   $141.80  
  Purchase #2 $137.52   12.623%   $154.8791   $154.88   $154.90   $154.90  
  Purchase #3 $167.45   6.351%   $178.0847   $178.08   $178.10   $178.10  
  Purchase #4 $28.60   5.561%   $30.1904   $30.19   $30.20   $30.20  
  Purchase #5 $244.95   3.393%   $253.2612   $253.26   $253.25   $253.30  
  Purchase #6 $39.33   11.218%   $43.742   $43.74   $43.75   $43.70  
  Purchase #7 $10.33   8.382%   $11.1959   $11.20   $11.20   $11.20  
  7 purchase totals = $752.98       $813.1935   $813.19   $813.25   $813.20