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 $43.94   6.592%   $46.8365   $46.84   $46.85   $46.80  
  Purchase #2 $227.53   8.854%   $247.6755   $247.68   $247.70   $247.70  
  Purchase #3 $110.53   4.577%   $115.589   $115.59   $115.60   $115.60  
  Purchase #4 $123.44   6.302%   $131.2192   $131.22   $131.20   $131.20  
  Purchase #5 $70.38   3.769%   $73.0326   $73.03   $73.05   $73.00  
  Purchase #6 $35.51   5.171%   $37.3462   $37.35   $37.35   $37.30  
  Purchase #7 $109.80   9.713%   $120.4649   $120.46   $120.45   $120.50  
  7 purchase totals = $721.13       $772.1639   $772.17   $772.20   $772.10