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 $188.89   6.815%   $201.7629   $201.76   $201.75   $201.80  
  Purchase #2 $159.68   5.160%   $167.9195   $167.92   $167.90   $167.90  
  Purchase #3 $213.90   11.274%   $238.0151   $238.02   $238.00   $238.00  
  Purchase #4 $32.50   4.331%   $33.9076   $33.91   $33.90   $33.90  
  Purchase #5 $47.57   3.565%   $49.2659   $49.27   $49.25   $49.30  
  Purchase #6 $170.43   9.617%   $186.8203   $186.82   $186.80   $186.80  
  Purchase #7 $133.97   10.719%   $148.3302   $148.33   $148.35   $148.30  
  7 purchase totals = $946.94       $1,026.0215   $1,026.03   $1,025.95   $1,026.00