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 $41.95   4.153%   $43.6922   $43.69   $43.70   $43.70  
  Purchase #2 $155.30   12.378%   $174.523   $174.52   $174.50   $174.50  
  Purchase #3 $136.62   4.506%   $142.7761   $142.78   $142.80   $142.80  
  Purchase #4 $112.34   7.555%   $120.8273   $120.83   $120.85   $120.80  
  Purchase #5 $79.64   10.148%   $87.7219   $87.72   $87.70   $87.70  
  Purchase #6 $35.93   3.449%   $37.1692   $37.17   $37.15   $37.20  
  Purchase #7 $37.31   4.473%   $38.9789   $38.98   $39.00   $39.00  
  7 purchase totals = $599.09       $645.6886   $645.69   $645.70   $645.70