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 $38.48   10.311%   $42.4477   $42.45   $42.45   $42.40  
  Purchase #2 $63.57   4.760%   $66.5959   $66.60   $66.60   $66.60  
  Purchase #3 $54.76   3.177%   $56.4997   $56.50   $56.50   $56.50  
  Purchase #4 $220.35   3.806%   $228.7365   $228.74   $228.75   $228.70  
  Purchase #5 $5.95   5.320%   $6.2665   $6.27   $6.25   $6.30  
  Purchase #6 $96.52   11.455%   $107.5764   $107.58   $107.60   $107.60  
  Purchase #7 $225.75   8.107%   $244.0516   $244.05   $244.05   $244.10  
  7 purchase totals = $705.38       $752.1743   $752.19   $752.20   $752.20