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 $112.54   4.858%   $118.0072   $118.01   $118.00   $118.00  
  Purchase #2 $228.97   5.713%   $242.0511   $242.05   $242.05   $242.10  
  Purchase #3 $235.80   9.679%   $258.6231   $258.62   $258.60   $258.60  
  Purchase #4 $148.75   11.487%   $165.8369   $165.84   $165.85   $165.80  
  Purchase #5 $81.61   11.837%   $91.2702   $91.27   $91.25   $91.30  
  Purchase #6 $61.94   12.864%   $69.908   $69.91   $69.90   $69.90  
  Purchase #7 $172.58   5.846%   $182.669   $182.67   $182.65   $182.70  
  7 purchase totals = $1,042.19       $1,128.3655   $1,128.37   $1,128.30   $1,128.40