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 $54.66   9.661%   $59.9407   $59.94   $59.95   $59.90  
  Purchase #2 $54.50   12.685%   $61.4133   $61.41   $61.40   $61.40  
  Purchase #3 $135.85   6.200%   $144.2727   $144.27   $144.25   $144.30  
  Purchase #4 $120.96   7.203%   $129.6727   $129.67   $129.65   $129.70  
  Purchase #5 $131.31   7.651%   $141.3565   $141.36   $141.35   $141.40  
  Purchase #6 $200.51   12.780%   $226.1352   $226.14   $226.15   $226.10  
  Purchase #7 $179.58   12.516%   $202.0562   $202.06   $202.05   $202.10  
  7 purchase totals = $877.37       $964.8473   $964.85   $964.80   $964.90