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 $224.69   7.282%   $241.0519   $241.05   $241.05   $241.10  
  Purchase #2 $161.51   3.796%   $167.6409   $167.64   $167.65   $167.60  
  Purchase #3 $16.71   4.851%   $17.5206   $17.52   $17.50   $17.50  
  Purchase #4 $50.88   8.527%   $55.2185   $55.22   $55.20   $55.20  
  Purchase #5 $53.79   12.157%   $60.3293   $60.33   $60.35   $60.30  
  Purchase #6 $149.29   11.269%   $166.1135   $166.11   $166.10   $166.10  
  Purchase #7 $43.35   8.364%   $46.9758   $46.98   $47.00   $47.00  
  7 purchase totals = $700.22       $754.8505   $754.85   $754.85   $754.80