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 $52.65   9.710%   $57.7623   $57.76   $57.75   $57.80  
  Purchase #2 $139.40   7.262%   $149.5232   $149.52   $149.50   $149.50  
  Purchase #3 $189.68   10.801%   $210.1673   $210.17   $210.15   $210.20  
  Purchase #4 $129.64   9.325%   $141.7289   $141.73   $141.75   $141.70  
  Purchase #5 $217.90   8.628%   $236.7004   $236.70   $236.70   $236.70  
  Purchase #6 $74.38   12.225%   $83.473   $83.47   $83.45   $83.50  
  Purchase #7 $121.55   11.314%   $135.3022   $135.30   $135.30   $135.30  
  7 purchase totals = $925.20       $1,014.6573   $1,014.65   $1,014.60   $1,014.70