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 $88.89   9.868%   $97.6617   $97.66   $97.65   $97.70  
  Purchase #2 $82.99   12.161%   $93.0824   $93.08   $93.10   $93.10  
  Purchase #3 $230.65   3.165%   $237.9501   $237.95   $237.95   $238.00  
  Purchase #4 $47.72   10.493%   $52.7273   $52.73   $52.75   $52.70  
  Purchase #5 $210.79   3.424%   $218.0074   $218.01   $218.00   $218.00  
  Purchase #6 $224.25   10.511%   $247.8209   $247.82   $247.80   $247.80  
  Purchase #7 $57.80   10.825%   $64.0569   $64.06   $64.05   $64.10  
  7 purchase totals = $943.09       $1,011.3067   $1,011.31   $1,011.30   $1,011.40