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 $30.93   10.116%   $34.0589   $34.06   $34.05   $34.10  
  Purchase #2 $123.83   9.565%   $135.6743   $135.67   $135.65   $135.70  
  Purchase #3 $25.82   13.456%   $29.2943   $29.29   $29.30   $29.30  
  Purchase #4 $58.38   12.261%   $65.538   $65.54   $65.55   $65.50  
  Purchase #5 $120.75   11.380%   $134.4914   $134.49   $134.50   $134.50  
  Purchase #6 $142.60   6.655%   $152.09   $152.09   $152.10   $152.10  
  Purchase #7 $229.90   11.231%   $255.7201   $255.72   $255.70   $255.70  
  7 purchase totals = $732.21       $806.8670   $806.86   $806.85   $806.90