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 $49.91   13.568%   $56.6818   $56.68   $56.70   $56.70  
  Purchase #2 $114.80   10.477%   $126.8276   $126.83   $126.85   $126.80  
  Purchase #3 $157.69   5.154%   $165.8173   $165.82   $165.80   $165.80  
  Purchase #4 $247.89   12.408%   $278.6482   $278.65   $278.65   $278.60  
  Purchase #5 $29.76   7.642%   $32.0343   $32.03   $32.05   $32.00  
  Purchase #6 $236.99   5.711%   $250.5245   $250.52   $250.50   $250.50  
  Purchase #7 $242.72   10.733%   $268.7711   $268.77   $268.75   $268.80  
  7 purchase totals = $1,079.76       $1,179.3048   $1,179.30   $1,179.30   $1,179.20