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 $32.58   6.873%   $34.8192   $34.82   $34.80   $34.80  
  Purchase #2 $62.46   4.210%   $65.0896   $65.09   $65.10   $65.10  
  Purchase #3 $29.86   4.808%   $31.2957   $31.30   $31.30   $31.30  
  Purchase #4 $61.38   11.254%   $68.2877   $68.29   $68.30   $68.30  
  Purchase #5 $167.55   13.585%   $190.3117   $190.31   $190.30   $190.30  
  Purchase #6 $178.87   12.582%   $201.3754   $201.38   $201.40   $201.40  
  Purchase #7 $62.55   13.558%   $71.0305   $71.03   $71.05   $71.00  
  7 purchase totals = $595.25       $662.2098   $662.22   $662.25   $662.20