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 $49.79   9.761%   $54.65   $54.65   $54.65   $54.70  
  Purchase #2 $218.46   7.155%   $234.0908   $234.09   $234.10   $234.10  
  Purchase #3 $117.86   8.143%   $127.4573   $127.46   $127.45   $127.50  
  Purchase #4 $180.87   12.482%   $203.4462   $203.45   $203.45   $203.40  
  Purchase #5 $105.87   11.654%   $118.2081   $118.21   $118.20   $118.20  
  Purchase #6 $193.46   3.734%   $200.6838   $200.68   $200.70   $200.70  
  Purchase #7 $82.95   3.391%   $85.7628   $85.76   $85.75   $85.80  
  7 purchase totals = $949.26       $1,024.2990   $1,024.30   $1,024.30   $1,024.40