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 $65.28   12.309%   $73.3153   $73.32   $73.30   $73.30  
  Purchase #2 $67.93   12.789%   $76.6176   $76.62   $76.60   $76.60  
  Purchase #3 $90.91   5.446%   $95.861   $95.86   $95.85   $95.90  
  Purchase #4 $142.74   8.653%   $155.0913   $155.09   $155.10   $155.10  
  Purchase #5 $235.79   9.270%   $257.6477   $257.65   $257.65   $257.60  
  Purchase #6 $203.62   3.159%   $210.0524   $210.05   $210.05   $210.10  
  Purchase #7 $92.67   12.809%   $104.5401   $104.54   $104.55   $104.50  
  7 purchase totals = $898.94       $973.1254   $973.13   $973.10   $973.10