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 $204.99   13.503%   $232.6698   $232.67   $232.65   $232.70  
  Purchase #2 $243.51   13.145%   $275.5194   $275.52   $275.50   $275.50  
  Purchase #3 $33.84   12.783%   $38.1658   $38.17   $38.15   $38.20  
  Purchase #4 $118.53   13.225%   $134.2056   $134.21   $134.20   $134.20  
  Purchase #5 $183.38   13.189%   $207.566   $207.57   $207.55   $207.60  
  Purchase #6 $55.94   4.698%   $58.5681   $58.57   $58.55   $58.60  
  Purchase #7 $73.31   5.464%   $77.3157   $77.32   $77.30   $77.30  
  7 purchase totals = $913.50       $1,024.0104   $1,024.03   $1,023.90   $1,024.10