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 $246.68   11.553%   $275.1789   $275.18   $275.20   $275.20  
  Purchase #2 $142.72   4.418%   $149.0254   $149.03   $149.05   $149.00  
  Purchase #3 $136.85   8.570%   $148.578   $148.58   $148.60   $148.60  
  Purchase #4 $165.66   11.221%   $184.2487   $184.25   $184.25   $184.20  
  Purchase #5 $118.32   6.671%   $126.2131   $126.21   $126.20   $126.20  
  Purchase #6 $44.84   10.452%   $49.5267   $49.53   $49.55   $49.50  
  Purchase #7 $22.32   5.705%   $23.5934   $23.59   $23.60   $23.60  
  7 purchase totals = $877.39       $956.3642   $956.37   $956.45   $956.30